Filmmaking would seem to be one of those subjects which you can't learn at home on your own, like medicine. Although some smaller aspects of the process, like screenwriting, might be learnable at home, the whole process of filmmaking seems to be just too big to fit in the garage. Anybody who's ever been to a film studio has seen the warehouse-sized studios where they work, along with the room-sized equipment that's used to piece the film together afterwards. And filmmaking requires the participation of so many people. The end credits of most movies list the names of hundreds of people. All in all, it seems to be too complicated and too major a project for amateurs. The only way to learn filmmaking must be to go to an expensive film school that might be hundreds of miles away.
Some websites challenge this presumption. Wikibooks' Movie Making Manual and the Film School Online both offer free filmmaking lessons. Both websites offer a detailed description of the filmmaking process from the original idea to postproduction and marketing, and the process isn't as overwhelming as it might seem. It isn't necessary to have a warehouse full of equipment, and the film can be edited on a laptop with a software program like FinalCut. It's also possible to get background music without having an orchestra in the living room. The Film School Online has numerous book recommendations which can supplement the filmmaking course.
These websites can be an enormous help to an aspiring filmmaker who wants to start with short films and to go on to larger projects as they gain experience. Anybody who wants more hands-on experience might attend a workshop in filmmaking as a supplement to self-study and still come out of it in a shorter time and with less debt than a traditional film school student. Anybody who's planning on going to film school anyway can be familiarized with filmmaking through these websites before making a commitment to it.
There seems to be some debate as to whether or not traditional film schools are worth it. Not long ago I found a forum in which some of the posters had been through film school but wouldn't go through it again. It's been argued that most film school graduates don't work as fimmakers, but as teachers in other film schools, and that it might be a better idea to put the money that would have been spent on film school into producing an independent film. An idea might be to combine independent study in filmmaking with business subjects, which aren't usually throroughly covered in the film schools. Whether one decides to go to a brick-and-mortar film school or not, it's a good idea to do one's own research as to how the film world works before making a final decision.