Author's Note: This is a very detailed guide on WhatsApp. So please go through this article patiently, there is lots of information to process. That being said, I update this post every month. So yes, everything is fresh.
Now why spend money on SMS when you already have a data plan?  This elevator pitch helped WhatsApp to attract 900 million users. And has now revolutionized the entire industry, by changing how people send SMS.

So How WhatsApp work?

Well, both parties need to install WhatsApp in order to send and receive messages. And this is what happens under the hood-
  1. The sender sends the message
  2. WhatsApp chat server receives the message and holds it. Now there are two possibilities
  3. One, if the receiver is connected to the internet, then WhatsApp server will deliver the message and (s)he will get push notifications
  4. Or, if the receiver is not connected to the internet, the server will hold the message and wait for him/her to connect

What does check marks mean

 -   message successfully delivered to the server  - message successfully delivered to the phone of your chat partner  - message successfully delivered and the recipient has read it

Can my partner read the messages even though there is ?

Single tick () is shown when your message is delivered to the server, but not to the receiver, as they might not be connected to the internet or their phone is dead. So No. If we go by the book, your chat partner have not read the message. So No. If we go by the book, your chat partner have not read the message. single tick on Whatsapp plus However, if your partner is using WhatsApp+ (or other modded version) then they can easily fake it. But how? Well, last time I used WhatsApp+, there was a 'single ticks enable' option, which shows a single check mark on the conversation even if it's read. 

What happens when you block someone on WhatsApp?

First, they cannot contact you via WhatsApp messenger. Second, they cannot see your update status or profile picture. However, they can still see your WhatsApp status and profile picture, by adding your contact number to another phone running WhatsApp. Provided, you have set these things to public, under WhatsApp privacy settings.

Can I send/receive messages on my phone's WhatsApp using Computer?

Yes, There are a couple of ways to do that. 1. You can mirror your Android screen to PC/MAC and use WhatsApp in real-time with Airdroid 3.(see gif ) 2. You can also use web.whatsapp.com. This is the official way to do that. I have written a step by step tutorial here. 3. But the best way is to install -- PushBullet android app. It will give you push notification on your browser. And you can also reply directly to your computer.

Can I send WhatsApp message using voice command?

Yes, you can. Say you are driving and don't have the time to stop and type the message, then simply open google now > say 'send a WhatsApp message to 'contact name'' followed by your message. send a whatsapp message with google now You need to confirm everything by saying yes, and that's it, your message will be sent without even opening the app. Similarly, to listen to your WhatsApp message, without opening the app, you can use Tasker.

Can I find out if someone has blocked me on WhatsApp?

NO, You can't. This is against WhatsApp's privacy policies but here is a workaround that works with 90% accuracy. Let say you are skeptical if your friend has blocked you on WhatsApp or not, then use these 3 indicators. 1. Last seen: If last seen remain the same for a long time, then this mean two things; either your friend is not using WhatsApp for a long time or you are blocked. This brings us to the next point. 2. Tick marks: Again if you send a message to your friends and it shows only a single tick, it means two things -- your friend has uninstalled WhatsApp or you are blocked. 3. Status & Profile Picture:  People often changes their WhatsApp's status/ DP. So take a note of the current WhatsApp's status and display picture of the suspect, now enter his/her number in other phone running WhatsApp and check status. If the status or profile picture has changed then you are blocked. Confirmed. But if status and profile picture remains the same then there are still chances of you getting blocked or suspect not using WhatsApp for a long time. And that's why I account for 90% accuracy.

Which platform does WhatsApp support?

It is available for a major platform like Android, iOS, windows, blackberry some Nokia Symbian S40 series, etc. You can even get WhatsApp on PC/Mac/Linux with emulators like bluestacks. WhatsApp also works on Wifi only tablet (iOS/Android) by sideloading the apk.

How WhatsApp make money?

WhatsApp is free, but not entirely. For instance, you get a free subscription for one year and after that, you have to pay small subscription fees. But now that Facebook has bought WhatsApp, they are no rush for monetization. (Cough Cough) Deep Pockets. WhatsApp also never spent money on advertisement. So that's saving. Now, Apparently, this is WhatsApp revenue model.
  • iOS user has to pay one-time subscription fees of .99$ at the time of their purchase and WhatsApp is one of the top paid apps in iTunes
  • Windows and Android users had to pay renewal fees of 1$ every year after their trial has expired
Note: If you are from India, then you may have noticed WhatsApp working fine even after 1 year. So apparently, WhatsApp is free in India and other African countries, due to low credit card penetration.
Update: They have completely removed the subscription fee. So, from now on -- WhatsApp is free, forever.

How to know if someone has added me on WhatsApp?

You will not know until they text you. It's like storing someone's mobile no in your phone book. If you don't call that person (s)he will never know.
But if that number is not on your contact list, then you get the option to either add or block them when you first received their message.

Can you hide last seen on WhatsApp?

Update: Now there is an option to hide last seen in WhatsApp by going to privacy setting. However, if you hide last seen on WhatsApp then you won't be able to see other person's last seen as well. Or you can use this simple workaround
  1. Turn off the data connectivity or your phone.
  2. Open WhatsApp and sent or read the message.
  3. Turn on internet connection after closing WhatsApp.
Related: Simple ways to hide last seen on WhatsApp.

Can I hide my online status?

hide whatsapp online status on whatsapp plus Yes, It is possible to hide online status by using WhatsApp plus. It is an unofficial mod of WhatsApp with many colorful options. Read more here. WhatsApp forbids the use of Third-Party Apps, by temporarily banning accounts who use WhatsApp plus or similar apps.

Can I chat with an international number using Whatsapp?

Yes, you can. Add the international no in the right format to your phone and refresh your WhatsApp. Voice calls work fine as well.

Can I recover deleted WhatsApp texts, photos, and videos?

Yes, WhatsApp takes back after every 24 hours. It's stored in/sdcard/WhatsApp/Databases/msgstore.db.crypt and stay there for a week after you delete the content. So if you have accidentally deleted your message re-installing the backup.

Can I use WhatsApp with one number on two phones?

No, WhatsApp works with one number - on one device. If you have installed WhatsApp on your phone and want but now want to use it on other devices. Then while installing WhatsApp on a second device, your WhatsApp account on the first device will automatically log out.

Can I use 2 WhatsApp account in one device?

Many people, having dual sim phone have this question. But sadly one can use WhatsApp - on one device - using one number - at any given time. Simply put 1. You can not use WhatsApp from one number on two different devices. 2. You can not use 2 WhatsApp account on one device. Update: However, there is a workaround. You can use Disa to run two WhatsApp on a single android phone or tablet. It's free, safe, do not violet WhatsApp terms and conditions (like OGWhatsApp) and no root require.
[youtube https://www.youtube.com/watch?v=AAW_8WtvfGU?rel=0&showinfo=0]

Can I log out from WhatsApp?

No, You can't. WhatsApp does not have a log out option. This is like in-built SMS service. However, one can always disconnect the internet or uninstall WhatsApp if you do not want to receive any message.

Is WhatsApp safe?

It depends. If the hacker has physical access to your device then he or she can install spyware on your device, and use it later. Moreover, if someone has your contact number then they can easily stalk you on WhatsApp. They can see your profile picture and your statues. If you don't want that, make sure to change 'who can see my profile' under privacy settings. Update: Apparently there is an app called WhatsDog, that can track the online activity of any mobile no. It can tell when the person is online. Although this app is no longer present on Google play one can easily find it on the web. So the bottom line is, don't post anything stupid that you may regret later. Read more: How to prevent WhatsApp hack

How to get a profile picture to fit in WhatsApp?

WhatsApp only allows square images for the profile picture. But using free apps like #square to add some padding to it. Or you can also take a screenshot of your picture and then add it your DP. If you have iOS or windows device, then read this

How to send new WhatsApp emoticons?

Emoticons can turn boring chats interesting. It helps us to express the feeling, that is difficult to express in text. If you like to insert cool meme and rage faces than check out this article.

How To Disable WhatsApp Notification in the status bar?

Goto Settings > Application Manager > WhatsApp > Turn off  'Show notifications'.  To disable WhatsApp notification only for group chat use the mute option.

Is there a way to send large files with WhatsApp?

The way to transfer large files over the internet is by using cloud storage like Dropbox or Google drive. Now, if the recipient is not tech savvy then you can use WhatsApp, but even with that, you can send a file up to 16 MB. Say you have to send a big video file with WhatsApp, for that, I suggest you compress the video first using handbrake and then use a free app called WhatsTools. It can send files up to 1 GB by integrating Google drive with WhatsApp.

Wait, there is more

I am a big fan of WhatsApp and like to know everything about it. If you are like me then be sure to check out the following article about WhatsApp.