CwCheats is a cheat format originally created for real hacked PSPs, not emulators, inspired by classic Action Replay codes. As such, it's very low-level and simple.
To use them, you have to download a cheat database and load it in cheat settings, which you can access from the pause menu in-game if this setting is enabled.
Unfortunately, these cheats are often a bit unstable - if a game starts crashing when you're using them, try a different cheat.