How do I find on my PC if I have an ethernet card installed on my PC?

OK
RIGHT click My Computer > Properties > Hardware Tab > Device Manager > Open network Adapters and see if you have on there.
Now bear in mind this may be an onboard controller rather than a separate card.

Or look on the back of the PC for something that looks like an oversized telephone jack.

How old is the PC? If its 3 years old or less it most likely has one.