@himew hello
You have several possibilities :

you connect a real keyboard and mouse (for all former computers, you should get a mouse/keyboard combo, it's quite usefull. Bluetooth ones work fine). or you edit a pad to keyboard file (.p2k file) where you can assign mouse button or keys to a button on your pad.
See this doc : https://recalbox.gitbook.io/documentation/v/francais/usage-avance/pad-to-keyboard (use a translator, the english version is still in progress)