Place magnets in the diagram. Each magnet has a positive and a negative pole, and adjacent squares cannot contain the same pole. The numbers give the number of plus and minus poles in each row and column. We will solve a small puzzle of this type as an example.
The top row contains two plus and two minus poles. Because the diagram is only four squares wide, everything has to be occupied by something. Optionally we can put circles in all of those squares with the right mouse button (click twice) to indicate that they are not empty. In the third column there are only plusses, from which we derive also the third square on the first row is a plus and its righthand neighbour, that accompanies him, a minus. Similarly the left two squares on the second row have to be occupied and because plusses can only touch minusses, we can fill in the entire upperleft quarter logically.
The second row and the first column are now complete, which we can indicate by filling the remainder of them with the right mouse button. To get to three occupied squares in the rightmost column every square that is still empty has to be filled with something, the same holds for the bottom row. The remainder of the third row must be empty and so its rightmost square must be the only plus that we will encounter there. The other three pieces of magnet we can fill in logically.