For SNES :
Get Snes9x GX 4.4.8
Extract it to the root of your sd card
Roms goes to sd:/snes9xgx/roms
For Genesis :
Get Genesis Plus GX 1.7.5
Extract the apps folder to the root of your sd card
Place roms in sd:/genplus/roms
If it doesn't exist create the folder
Can be placed on USB too