If the 'box' is normal size, there shouldn't be much trouble, but open the box and look for-
A bay large enough to contain the HD
Ideally two ribbon cables, one to the present HD and one to any CD device. If they share a cable then look for another socket on the motherboard parallel to the one already in use.
A spare power lead (red yellow and black) is handy but like a new ribbon cable is easy to buy almost anywhere.
A new HD is really a matter of screwing it in place, connecting the right cables, and then making sure the computer realises it is there, before using software to prepare it for a life of service! :o)