To play games you need either a PS3 DVD or you need a .ISO file from the game. To Start a game you need to select which you want to use, in File > Open file > then pick "From file" or DVD.
You can use netplay through the emulator! However, you cant play on the official PSN(PlayStation Network) You can play on LAN or host your own servers. Please note this is still in its very beta version and have bugs, but we are on the right track!