Open the MM filemanager and use this to create a folder on HDD0... called ROMS. Create a folder in here for your SNES roms, how bout we name this folder SNES. Open this folder then open your dev_usb00x (x= 0,6 or whatever port your flashdrive is in) Find your roms and copy them to your SNES folder. Launch your emulator and you may need to set up the start up path where your roms are located.
I may have missed a few steps since it's been an age since I've set up Retroarch(if you're not using retroarch you need to switch ASAP you wont regret ).
will notice this thread and steer you in the right direction where I may have gone astray