How do you build a model glider?

Usually you can find kits for them. You cut out the pieces of Balsa wood and glue them together as per the instructions. Or design your own. Then you can cover the wings (if they have ribs not just a flat piece of wood) with some sort of cling film usually using a heat gun (or a blowdryer) to get out the wrinkles. Make sure you use strong enough glue to hold the pieces together. Search around and you should be able to find some sites that sell everything you need and might even have tutorials.