Desktop PCs typically, and certainly those of 'a certain age' would not have a wireless card installed. If one has been added subsequently, you will see an aerial stick (or two) sticking out from the back of the PC, and you will almost certainly also have a CD with the drivers for it.
You can find out more about the basic machine and obtain up-to-date drivers at click here you need to get a wireless connection, you can either buy a USB dongle or a wireless card:
if you have a spare USB port, you simply plug it in
you need to open up the box and connect a wireless card to a spare PCI connector - see click here further advice