What's wrong with my car?!??!???

Hey guys once again I'm hear to seek the wise counsel of HS board monkeys. I tried to crank up my car today and it wouldn't crank. I thought it was out of batteries so I went and got an new one, an auto zone battery. And now the car would crank, but it dies on me every time I stop giving it gas-like when I shift gears or step on the breaks. Any thoughts on what might be wrong? and would I be able to fix it with basic tools? Thanks.