What is the purpose of a window? A window is basically a hole that was cut into your house filled with glass. Giving you a view of the outside world while giving light a place to reach the inside of the home. The most important things you need a window to do is allow the most light in while not allowing the outside world in with it. You also want to be able to see the outside world clearly yet keep what is inside from getting out as in your heating and cooling. While these are the most important things you also want a window that looks nice too.