To light a Christmas tree, start by finding a strand of Christmas lights that matches the size of your tree and the number of bulbs you want to use. Make sure the lights are designed for indoor or outdoor use, depending on where you'll be putting the tree. Then, carefully unwrap the lights and plug them in to make sure they work properly. Once they're ready to go, begin wrapping the lights around the tree, starting at the top and working your way down. Be sure to evenly distribute the bulbs so the tree looks even and bright.