Place tents in the empty squares in such a way that:
Click in a square to place or remove a tent. Right-click to mark a square as empty (not a tent). Right-click and drag along a row or column to mark many squares at once as empty.
Warning '!' marks appear to indicate adjacent tents. Numbers round the edge of the grid light up red to indicate they do not match the number of tents in the row. Groups of tents light up red to indicate that they have too few trees between them, and vice versa.