Whenever you open the WhatsApp messaging application on your mobile device, your last seen counter is updated to reflect that.
What this means is that any contact that you have in WhatsApp sees when you were online the last time when they open the app on their device.
While that may not be an issue all of the time, you may sometimes want to avoid that your last online date and time is updated, for instance if you do not want someone to know that you read their message, or that you did not reply to their message the moment you read it.
It is possible to read messages on WhatsApp without being shown as online to others. I have outlined how that is done without software before.
Basically, you disable all network connections before you open the WhatsApp program. You can read all messages that have been downloaded to your system, and since you do not have a network connection at that time, your last seen date and time won't be updated as a consequence.
WhatsApp Ghost is a useful application for Android devices that automates that process for you. Instead of having to disable the network connections manually, it does so automatically for you when you run the software.
Even better, it displays all of your contacts and messages right after you run the Ghost application, so that you can read the messages comfortably without having to tap again to start WhatsApp manually.
Once you have read all the messages that you wanted to read, you can hit the back button. This displays a basic interface which you can use to turn off Ghost Mode again. If you do, all network connections are established again.
The WhatsApp Ghost application terminates Wi-Fi and wireless connections on your mobile device and launches the original WhatsApp application afterwards.
The only thing you have to change is to tap on the Ghost application icon when you want to use it instead of on the WhatsApp icon. Everything else remains the same.
Note that it hides the last seen status of your WhatsApp contacts, but that cannot be changed unfortunately and is not caused by the app but by how the WhatsApp application handles this.
WhatsApp Ghost is a handy app for Android if you want to check WhatsApp messages regularly without being shown as online to contacts.
If that is something that you only need to do occasionally, then it may make sense to use the manual way instead, as it avoids having to install another application on your device that you do not use a lot.