You must escape from check on your first move of a turn. If two pawns are advanced two spaces, both may be captured en passant on a turn. The queen can only capture pawns. The rook captures pawns, knights and bishops. Knights and bishops capture pawns, knights, bishops and rooks.
All pieces can check and checkmate, and kings still capture everything, as per usual.
The pieces, the setup and the board are the same as in standard chess. A pawn cannot be moved to the first or last rank. The King moves as in normal chess. It sounds quite silly that all pieces can be moved to any desired empty square but it works and its a fun game. In the late 80's I created a chess variant called Mage.