Click and drag with your mouse on the nodes, and get the laser through to all of the circles before the counter on the bomb reaches zero and explodes. Keep in mind though, certain nodes can not be moved - if you encounter one of these, focus on manipulating the other node towards your goal. Sometimes you will be dealing with just a single node in a level, instead of multiples. These nodes will shoot off a beam in only one direction. However, you can utilize mirrors to your advantage - when the laser hits a mirror, it will change the direction of it. The mirrors themselves are also draggable - keep this in mind when you race the clock trying to solve the puzzles. There are blue nodes in the game - these nodes curve instead of making a straight line. Later levels will require you to use both types of lasers and nodes as well as things such as mirrors - all while you race against the limited amount of time on the clock. It will take some seriously sharp wits to solve these puzzles - but that makes them all that much more satisfying once you are finally able to solve one that has been leaving you stumped.