Being essentially the only animal on earth using something called "clothes" it is today widely believed to be the reason for their wide distribution in different habitats. Clothes seem to be a replacement for fur, which are the most commonly used thermal protection devices used by other mammals (but there are some mammals that have started to use clothes when interacting with humans, such as dogs).
Humans have mastered the techniques of tool use, which may explain the rather advanced societies they have developed, called cities. However they are still on a quite low technical level. They have yet to invent spacecrafts for interstellar travel (although it is at the point very unlikley to happen within the nearest 1000 years).
Humans as all mammals are essentially fish that left the sea for land many millions of years ago. Some of the mammals later left land to reunite with their old habitat, wales, seals and manatees. These animals are by some observers often considered as the biggest quitters in the history of life on earth.