Unregistered

Well here's the story. I was driving on the interstate when my car reved. i hit the gas and it reved louder and started to slow down. i pulled to the side of the road and shut it off. Turned it back on and put it into gear and tried to drive off. But it just sat there and reved up. In any gear it does the samething. i need help i know nothing about cars or what i should do. is it the transmission. and if so what should i replase.