Hello.
Have you looked at the app drawer / list using the app icon in the dock. (Android language!
).
If you have a Samsung it may be on an icon folder (tray), labelled Samsung, or try Galaxy Plus, I can't remember which.
You can look in Settings - Apps /Applications Manager - All to see if it's there, but it's unlikely to be missing.
Come back if you need more help, but let us know the device.