Just download a ROM file (can get them from many different ROM websites) and put it in a folder that's easy to remember. I usually put all my ROMs in a ROM folder and have seperate folders inside that one for different systems.
It usually comes as a .zip file (ex: castlevania.zip).......when you load up the emulator you just navigate to the folder where you put your ROMs and it should load up when tapped
It usually comes as a .zip file (ex: castlevania.zip).......when you load up the emulator you just navigate to the folder where you put your ROMs and it should load up when tapped