Android Question

I just bought a Samsung Galaxy s2 Skyrocket off of Amazon and I didn't think to see if it came with a Sim card and it didnt. So Im about to order one from the carrier but I don't know what kind of sim card it takes. Their web site advertises micro sim cards and sim card. But I dont know if it takes a micro or not. I dont know the difference and their are not directions! Please help! What kind of sim card does a samsung galaxy s2 skyrocket take?