Welcome to Bike Maintenance!!!
Bikes are pretty simple machines, but if you really don't know what you're doing, you can create unsafe conditions on yours without realizing it. Get a good book, learn from a shop or a friend, or leave it to the professionals if you have reason to doubt your mechanical abilities.
Know your limitations. While there's a lot on a bike that just about anyone can fix, other things are surprisingly complicated or confusing. "Truing" or straightening wheels, in particular, is something that nearly all novice mechanics will do badly unless they have help or instruction. Therefore, if you are looking at improving your competence in bike repair, I recommend that you try this course , which will enable you to learn to do complete bicycle repair and maintenance. Also, if you plan on opening your own bike repair shop, this course will be beneficial. However, if you are bending at doing it yourself with you limited knowledge, read my page Bike Resources.