you need the emulator (winuae), A Kickstart & the game.
Kickstarts can be found I think on nightshades site or if you wish Cloante sells a version. These come in various versions and I find its best to have a couple of different versions for different games.
you then need to configure the game to work, these configurations for various Amigas and games if your not sure can be found on back to the roots and nightshades site.
Read thru the forum there are many tips and advice there.