fics is the free internet chess server. Xboard is a chess client. This is how you make them work together:
I usually use xboard. It's possible to, e.g., log on to servers like ICC and FICS, which I find to be good places to play chess at.
ICC: "xboard -ics -icshost chessclub.com"
FICS: "xboard -ics -icshost freechess.org"