Park Tools Repair help is a good place to start. Click on the bike map for your trouble spot and the directions provided are very clear. You don't necessarily have to follow all of the directions under each topic...limit screws which have already been set and don't need to be reset are a prime example...but you can get through most of it.

You also learn by doing. I took a class on bicycle mechanics long ago but most of what I learned was through just doing the work. Bikes are easy to understand and work on, although there are a lot of small details. Just keep working on the bike. Long ago I heard someone say that the difference between a inexperienced mechanic and a master mechanic is the number of parts they have ruined. A master mechanic has ruined far more...but they learned from the experience.