Rust is a chemical reaction that takes place when iron (such as is contained in the steel that your car is probably made of) is exposed to oxygen and moisture. Road salt can also accelerate this process. Your vehicles paint, in addition to making your car look good, also serves as a barrier to prevent such rust. As the dings and chips add up, so do the chances of rust getting a foot-hold in the metal of your car. In an accelerated state, battling that rust can seem never-ending, but there are ways to try and keep it at bay.
There are various products to remove rust which claim to spray on clear and only react with the rusted parts. This is ideal if your repair plans don’t include a full respray, as they do not cause any alteration to the surrounding paint.
Rust converters work as the name implies by chemically converting the rust to a stable state in order to stop the rust from spreading. This doesn't remove the rust, but it may be good enough if you only plan to stop the rust from advancing. It will likely require further bodywork if you plan to paint over the affected area. There are also various paint products which allow you to paint or spray over and isolate the rust rather than remove it.
More aggressive methods of vehicle rust removal do so by abrasive means. That could be a wire brush, sandpaper, or a grinder. When sanding out the rusty metal it’s best to immediately seal, prime (perhaps with a self-etching or epoxy primer) and paint the area to prevent the rusting process from reoccurring. You'll probably need sandpaper of different grits to get a smooth enough finish.
In extreme cases, car rust may have eaten completely through the panel. Frequently this sort of repair is going to require that the affected area be cut out completely to remove any trace and new metal welded in its place. Patch panels are available for many popular models to help simplify this process. Hopefully it hasn’t progressed this far on your car, but if you love your car there is always a way it can be repaired.
It's best to consult a body shop when considering some of the more advanced rust treatment techniques. But, rust prevention doesn't always have to be involved. Sometimes simply washing your car more frequently can be an effective rust inhibitor as it helps to remove dirt and road salt that can trap moisture close to the body and serve to fuel additional rust. And, don't forget to touch-up chips before they become rust.