I've decided to show you in a video how to use boolean and extrude and what they do:
With boolean you can cut an object into another object. So you can easily create 3d windows or whatever you want. Extrude is also very helpful (especially on car editing) as you can see in this video i made the roof with extruce tool!
If you have any questions or whises, please mail me (firstname.lastname@example.org) or comment here!