How do i tell whats wrong with my car?

My 1995 Chevrolet Cavalier today didn't start. i went out to drive to school like every day. but as i went to start it it made the same noises it always does. the little revving noise. only difference was it didnt turn over and start like usual. i tried again and again with no effect. i didnt want to flood it so i only tried hitting the gas like people told me once or twice but there was no effect. idk if the batterys dead or what. we replaced the engine and transmission when we first got it so it shouldnt be them. any answers?