To create your own superhero, come up with the superhero's gimmick, determine a backstory and sketch character designs. While many superheroes have common attributes, people creating them aren't bound by any particular rules.
Almost all superheroes have some sort of gimmick, and many fall under certain archetypes. Johnny Quick and the Flash, for example, are known for their superhuman speed, while Batman and the Green Arrow are know for creative weapon use. Reading through various archetypes can help people think of a clever gimmick.
Heroes in all forms of fiction typically have backstories. These stories outline how the superhero gained powers and often outline what weaknesses the superhero has. In addition, superheroes generally have a motivation for performing their acts of heroism: Batman wishes to make the streets safer after his parents were murdered, for example. This backstory helps create a character readers empathize with.
Perhaps the most important part of creating a superhero is creating the illustrations. Drawing is difficult, so people with minimal experience might want to follow guides for drawing existing superheroes for practice. While superheroes often have exaggerated physical characteristics, most fall close to the typical human range with a few tweaks. The details of the illustrations are important as well; creators need to decide on a color scheme and an appropriate costume.