Step 1: Tube and Tire change.
To put the tire back on, You pretty much just reverse the process. It's really simple.
Step 2: Brake Work.
Now I will show you how to replace the brake pads. You will need allen wrenches and possibly a pair of pliers. Replacing brake pads is pretty self explanatory. There is a nut that can be loosened with an allen wrench, and a lot of weird washers. The only hard part is remembering how the washers went back together. All you do is take off the nut, washers and, brake pads, and put on the new ones. Align the brake pads with the wheel as close as you can. This will increase stopping power and thus safety. Tada!! Now you know about brakes!!
Step 3: Shifters and Derrauillers
Shifters are very easy to replace. Remove the grips, brake handle, and old shifter, and put it all back together with the new shifters.
The hard part is adjusting the deraiullers, (Does anybody know how to spell that??) On deraiullers there are two small screws called limit screws,these screws adjust how far the deraiuller can move. One of them is touching a piece of metal, loosen or tighten that screw to adjust the deraiuller. I have yet to master them so it might not be best to learn from me. As I said , it is probably best to search this subject.