By doing this:
----O
you create a reverse loop. Try a search on "wiring reverse loop" or something like that.
Are you using DC (powerpack that comes with a train set) or DCC (digital command control)? I will assume DC, since you just got a set. So for conventional DC, you will need to wire in some electrical switches to change the polarity of the track. It is not too difficult, but you do have to be careful to get it right, or risk frying your loco and/or powerpack.
Andrew