Fill each domino shape with either a magnet (consisting of a + and − pole) or a neutral domino (green).
The number of + poles that in each row and column must match the numbers along the top and left; the number of − poles must match the numbers along the bottom and right. Two + poles may not be orthogonally adjacent to each other, and similarly two − poles.
Left-click a domino to toggle it between being empty and being a magnet (the + is placed in the end you click). Right-click to toggle between empty, neutral, and a ?? mark indicating that you're sure it's a magnet but don't yet know which way round it goes.
Left-click a clue to mark it as done (grey it out). To unmark a clue as done, left-click it again.