Gamecube games for dolphin emulators dont work?

when ever i download a game that should work for the dolphin emulator it doesnt work up and a message pops up and says somthing. when i look at the file it shows up like a piece of paper for the picture instead of the zip file that shows up for my n64 and snes roms. It could be the place i download from but i dought it because other people said it worked and ive tried so many things. if any one could help id appreciate it.