I use eboard to play chess in FICS (free internet chess server)
you must make an account in
www.freechess.org (FICS) and used the id and pass from here to use in eboard
indicate is to install the timeseal for eboard
for xboard,to play against a chess engine,you need an chess engine like crafty,toga2,stockfish etc
for UCI chess engines(like toga2,stockfish) you need an program named polyglot
easy is to install crafty and play with xboard and start like this:
xboard -fcp crafty