Just put it in, boot and answer the questions and follow the instructions. This will return the PC to the state it was in when it left the factory (assuming it's a standard restore disk, which is most likely). Probably they did this already or the new hard disk would be empty.

Then install everything you like to get the machine in the state you want it to be. That includes installing all programs you need (such as antivirus and spyware protection) and a driver for your printer. If you can't do it yourself, find a friend or family who can or pay a shop to do it.