Draw horizontal or vertical bridges to link up all the islands. Bridges may be single or double; they may not cross; the islands must all end up connected to each other; the number in each island must match the number of bridges that end at that island (counting double bridges as two). Note that loops of bridges are permitted.
Click on an island and drag left, right, up or down to draw a bridge to the next island in that direction. Do the same again to create a double bridge, and again to remove the bridge if you change your mind. Click on an island without dragging to mark the island as completed once you think you have placed all its bridges.