Cheat Engine comes with a tutorial that explains the basics on how to use cheat engine.
It explains memory scanning, debugging, coding, and how to think when writing code
If you closed the tutorial the first time, you can always reopen it using the help menu.
The first step you should always do:
First click the flashing computer icon top left, and then target the process you're interested in (or connect to an android device running ceserver as root in your local network and then target the process you're interested in)