Setting up an iphone sim card?

I got an iphone 4 online but i have no idea how to activate the sim card and you don't get many details with the phone and i didn't even get a thing with the sim card telling me what the actual mobile number is iv hooked the phone up to itunes and everything but the sim card still won't let me ring anyone can anyone help me please

Well… Where did you get the SIM card? Which carrier provided the card? They should have assigned you a number with the card. Then you just pop the card in the phone and turn it on.iTunes has nothing to do with it. SIM cards are activated by the carrier.