To put Christmas lights on a Christmas tree, start by gathering the lights and plugging them into an electrical outlet. Next, determine the layout for your lights, whether you want to wrap them around the tree or place them in an eye-catching pattern. Then, start at the bottom of the tree and work your way up, making sure the lights are evenly spaced and not tangled. You can use extra ties or hooks to secure the lights to the branches if needed. Finally, turn the lights on and enjoy the festive glow!