Initially you have matches on 4 rows (7, 5, 3 and 1 matches by default, modifiable by the preferences). Players play one after other. When his turn, the player must remove at least one match, but he can remove as many as he wants in a single row, and even all the matches of the row.
Game stops when all matches have been removed. The player who has removed the last match is the loser (except if changing the preferences you have decided otherwise).