I need help, please

[Abbanon]

Is the controller USB by default? Or are you using a Gamecube-to-USB adapter like Mayflash?
Either way, you might need to install specific drivers.

I personally have a Mayflash adapter for Gamecube-to-USB, installed the drivers, and it works with PPSSPP perfectly fine.
I don't recommend using a Gamecube controller for Monster Hunter though - it really messes with muscle memory.

Also, what OS are you on? Windows, Mac, or Linux?