Ground school is the academic or classroom portion of flight training. The Federal Aviation Regulations (commonly known in the flying world as FARs) states the minimum information that must be covered under "aeronautical knowledge". An authorized instructor must certify and log that you have either been taught this information or have completed a home-study course. So do you want to save some money to spend on aviation fuel? All you have to do is study the book yourself! 

"Which book," you might ask? The FAA doesn't actually tell you which book. You could watch YouTube videos, get a book from a company like Gleim or Jeppesen, or you use the free books provided by the FAA.  I have used them all, and I'll tell you Gleim and Jeppesen are very similar. They are written for, and target the student pilot. The FAA's Pilot's Handbook of Aeronautical Knowledge is more written as a reference manual for people who are already pilots. But there are two things that I really like about it. First, it is not only free, but it is updated regularly by the FAA. And Second, and probably more importantly, it teaches student pilots to dig into the source material. "Because it says so in Gleim or Jeppesen" is not a great answer, but FAA publications such as the FAR/AIM are actually source documents with authority.  

So Below you will find the outline I use for my ground school class. This is updated as needed, and maybe even someday I'll put it all on YouTube so you can watch me explain things for free. But there are probably much funnier, or at least better looking instructors already out there. So hopefully this helps, and please provide any feedback that you have!