just google that cpu
"athlon xp 2400+"
better is to know what mobo, and look that up at the manufacturers site - and download the manual, or the specs
but it's pretty old and the cost of ram might be more than it's worth.
still - it's a good exercise to search out the info - cos then you can search out anything
which means you can make educated decisions for your own needs.
also find a bargain site where they sell used parts - and pick up some old ram for a few dollars. make an offer. be cheap.
take the pc with you so you can plug it in and see it work.
first do the research.