I learnt to reset my gears by learning by doing, asking on here and i got a book. Cant remember the name of it, but it explains how the part works and how to maintain it and adjust it and stuff.
I also had an old bike that didnt work too well, that i played about with, which taught me how to do things. I found it hard to do stuff on my bike because i didnt want to do something, then not have the bike to go out on the next day. So having a seperate bike ment i could take my time, learn to do it, then do it again just to make sure.
Learn by doing. Its more fun then taking it to a bike shop. And if you do it right and make it look like you know what your doing, your well away.