You play White with the full set of sixteen pieces. Black has a king, eight pawns and one bishop. Checkmate the black king to win. This is real chess with real rules, so castling, en passant and promotion all work, and a pawn that reaches the far side becomes a queen.
A bishop only ever sees one colour of square. A piece standing on the other colour is safe from it, so attack the bishop with pieces it can't reach, and keep an eye on the pawns and the black king too.
Three levels: on easy Black moves at random, on medium it usually grabs a piece you leave undefended, and on hard a real chess engine looks a few moves ahead. Win once for a silver star, and ten times without undo for a gold one.