Why wont my car turn over?

Hello, I have a 98 Pontiac Firebird. I bought it like a month ago. Had to wait until we can drive it. It ran good when they brought it to us. But when we finally went out to drive it, it wouldnt start or turn over. Im not a car mechanic type so I dont know what could be wrong with it. I searched around and alot say the battery... when I get it and turn the key a little, the radio and everything work. The "check Gauges" sign light up, what could that be? Then when I turn it to start up, it just like thuds a little not even trying to turn over and the radio goes off when I try to start it.. Any one know what it might be? The Battery? starter? or something else? what does "check Gauges" mean, what do I check?