There are many styles of comic books. The medium as a whole is often seen as "for kids," but it's much more than that. Some are wholesome, some are not. Some are indeed "for kids," but others contain enough nudity and graphic violence to warrant a warning label. In the American comics market, though, one genre reigns supreme - the superhero comic. These are the ones that get the action figures, the blockbuster movies and the cosplaying convention-goers.
The birth of the superhero comic could be said to have started with the 1938 debut of Superman. He had his predecessors, to be sure, but Supes is without a doubt the most recognizable superhero of them all. He had all of the traits that are now seen in most superhero comics, and he's still going strong over 70 years later.
A superhero is the quintessential "good guy," but what makes a superhero? Usually, they have superhuman powers and abilities. Some can fly, some are super-strong and some can shoot energy from their hands. The range of powers seen in superhero comics is nearly infinite, limited only by the imagination. Usually these powers are innate, as with Wolverine's healing factor, but they can also be artificial. Batman uses technology planning and smarts to win, while Iron Man built himself a super-powered suit.
Ah, but what separates the superhero from the other crucial part of the genre, the super-villain? Superheroes have a firm moral fiber. For many of them, this means they refrain from killing even their most bitter enemies. They fight crime and villainy because it's right, not for pay. Most superheroes seem to be fabulously rich already.
Another common aspect of superhero comics is a thematic motif. Spider-man, Batman and Hawkeye are prime examples of this. If there's no theme, there's at least a costume. Heroes often wear costumes not for themselves, but to protect their loved ones from retaliation. They certainly don't do it for themselves - it would hardly make fighting easier to do it in restricting clothing without a single pocket for your Batmobile keys.