Go to office hours. If there are any TA's or older grad students who have taken the same class, ask them about what you don't understand. Usually they went through what you did, so they know how to explain and conceptualize things. Don't fall behind. And it does get better....a lot of classes overlap, so by winter you'll be seeing things again and it'll be easier.

Edit: Oh, and doing homework and surfing HAN doesn't work so hot. Trust me h: