If you do not see WhatsApp on your home screen, the icon might be hidden.
You may need to reboot your device by removing the battery if you installed or updated WhatsApp from App World.
If the previous step did not resolve the problem, ensure that the WhatsApp icon hasn't been hidden or moved to another folder. You can select Show All Icons by pressing the button on the main device screen to see all icons, including hidden ones.
If your WhatsApp icon is grey or transparent, you need to press the button and select Unhide icon.