Some garage doors are much more difficult to adjust and repair than others- successful garage door repair requires a feel for the difference. Some spring assemblies can be deadly. The best bet for a do-it-yourselfer is to go with a lighter door that has a simpler spring mechanism.
Looking at all the individual parts that make up a working garage door and electric garage door opener can be downright overwhelming. You'll have dozens of metal bits splayed all over your garage: the huge metal tracks, the rollers, the hinges, the fasteners, the nuts, the bolts, the cables, springs, and handles, the struts, the panels themselves, and enough screws to frighten even the most cocksure repairman.
But some garage door manufactueres have deigned to makekits for those of us who like to instlall things on out own, and they are getting more and more user-friendly every year.
The best place to start is obviously the instructions- familiarize yourself with all the parts and where they go and th physics of how the door aught to work.
But here's the catch- if you can't even understand the directions, you definitely should be calling in the big guns. That's when you need to put down your pride for a moment, pick up the phone, and call a professional garage door installation company.