You have to download the games (which you must already own for legal reasons) to your pc. It is a zip file.
Create a directory on your SD card called games ir something and put the zip file there.
Then when you open snesoid, browse to games and select the file. If snesoid is the same as genesoid (its teh same developer) then it should be able to play directly from the zip file. If you have problems unzip the .bin or .smd file inside to that location and try again.