I got a game key from a friend since they don't own a PC, I have the option to download the installer online but when I open said installer it opens the Galaxy app and nothing happens from there. I don't have a download shelf and nor do I have the option to enable the shelf. Do I now just have to download the game in parts via my internet browser? Is this normal? I cant find any help on the forums so had to make an inquiry here.

This sounds like something to write to support about rather than something GOG users can help with.