One player is the rat, trying to move across the board's yellow squares to one of the cheese squares. The other player is the trapper, trying to completely surround and trap the rat.
The rat player moves first, rolling the die and moving from the start square orthogonally that many squares. Then the trapper rolls the die and places that many fences on the board in the slots between squares. There are 5 total fences in the game. Once all fences have been placed, the trapper must use the already placed fences.
The game ends when either the rat cannot move, or the rat reaches a cheese square on the opposite end of the board.
The d6 is missing, so I'm unsure of its marks, but the instructions indicate that it has at least 1 blank spot, and it's reasonable to assume it goes no higher than 3, since a higher roll would be an automatic win for the trapper.