GSM Interfacing with 8051

Hello,
I want to interface GSM mobile with 8051. But I don't know how I start my work. Can You please suggest me which 1step should I take? What are AT commands Is there any software used for this? please guide me this is the main task in my Final Year Project. Hope you will guide me soon.. Thanks in Advance

Is there any One who can Help me please...

first buy a GSM module.then learn how to turn on it.and connect to computer by serial port,and you ban test it.sent "AT" ENTER.and see what's going on.