Panel beating is the fine "art" of fixing the paneling (also known as "body") on a car after an accident or other event (such as a storm). It's known as "panel beating" because in most cases one has to quite literally beat the paneling back into it's original shape. This can be done using a variety of tools that are common in the majority of professional automobile repair shops. The skill range required for reforming the paneling of a car ranges from novice to extraordinary, depending on the condition of the paneling or automobile in question.
Panel beaters (aka car-body repairmen) use a wide variety of skillful techniques (and some non-skillful ones, too). These techniques can range from planishing, welding, and filling, to name a small amount. The majority of more severe accidents sometimes require the panel beater to repair a section of the paneling. In worse cases they may have to replace certain parts.
The skill and tools required to do this can also vary, but the end result normally looks smooth and matches the car's original shape. Panel beaters are also able to do vehicle restorations (which can be a difficult and costly task), paint preparations, small electrical repairs, small mechanical repairs, and car detailing. Using this small range of what a panel beater can do, it is also not beyond their skill or knowledge to do a vast majority of other things not listed. This is true for the more skilled repairmen that can do anything from panel beating to building an engine from the ground up. Although the predominant amount of panel beaters tend to be more specialized and less experienced in a wide variety of fields, it's not uncommon for there to be a "jerk of all trades" amongst them.
For an example of panel beater specialization; they can be specialized in a particular vocation. Road vehicles (automobiles such as vans, 4WDs, etc) being the predominant parties. They may also extend to different types of transportation such as a motorcycle, trucks and buses, trailers, aircraft, and many more. They do this by using a wide assortment of tools. The tools a panel beater might use may consist of a simple arc-welder and sander, or the more expensive ones such as a magnetic dent remover. These tools can take some skill and time to learn, and most of them aren't mere playthings that one can suddenly decide to buy, pick up, and use. They require training (and some of them college training) and time to learn to use. So it's not surprising for the majority of people to take their cars to professionals rather than attempt to repair it themselves.