You have got to be kidding.
This was explained to you so many times that I think we've all lost count. The information is in the manual, plain as day, crystal clear!
1) Create a new folder on your Sansa. Call it "Game Boy" or something.
2) Copy your ROMs into that folder. They must have a .gb or .gbc extention.
3) Start Rockbox.
4) Navigate to that Game Boy folder in the file view. Pretend that you're looking for music in it. Select the folder.
5) You should see your Game Boy ROMs in the folder. Pick the one you want to play and press "Select".
6) That's it! Rockboy starts up.
Now is that so complicated?