External Hard Drive?

My computer says that I have the heart drive. So I went out and bought a hd external (westerndigital mybook critical edition 160GB) because I installed everything I had to do was plug it, but I am not sure what to do after. I have a hard heart, and I think I could go and spend more things in my shoes. Hd and i really dont know what to do. It came with two software things that I can use for thirty days. Was an auto sync the other was automatic backup. And it was delivered with a software also google. But I do not know at all what this does, ijust want to be able to add more to my hard disk drive c is not as rich and what not. This computer is an old, my sisters (she graduated in 2004), she got a new Christmas. And it has lots of pictures and stuff in it and i was wondering if i could take all of her stuff and throw it at the post office. Hd and then free my computer so I can still use itunes and add music on my computer without a hard c stuff, but still be able to reach its substance