For some minor damage, dent removers with a suction cup will work. However, most of the time you'll have to fill in the dent and repaint the affected area. Filling a dent with body filler isn't that difficult, but it's hard to do it right. With a lot of patience and a willingness to revisit the damaged area again and again until it's OK, you can do a very good repair with a body filler.
Once the dent is full and dry, it's time to paint. You can always save some money by repairing the body yourself and then having the painting done by a professional auto shop. Before you dive into body repair and learn how to do it in your driveway, evaluate your skill level. If you want a perfect repair, find a really good body shop (get a recommendation from someone who has done business with them) and repair your vehicle properly.
Dents on doors, scratches on the bumper, scratches - these are all things that you may have the opportunity to repair yourself. If you need to touch up an area of paint, the auto parts store sells a wide variety of car paints that should look pretty good. Just know that you may have to do it more than once to get a satisfactory result and that you probably won't end up with a result as good as a professional repair.
