Two black wires in the box would be a hot from the supply and a switched hot to the load. If the timer has only two wires then it should be pretty easy to just connect them. If they are marked line and load then you would have to hook the wire for line to the wire in the box that is always hot from the supply and the other to the wire marked load. If you are still unsure then it really is not a job for you alone, enlist the help of someone with a bit more experience or even an electrician.
