Creepers are mobs that can live in the day or night, so they do not burn up in the sun. Creepers can explode if you get anywhere near them. But if you kill them, they are made of gunpowder, which is used to craft TNT.
The creeper is a hostile mob that will ambush players and explode, causing damage to the player and the surrounding blocksand entities. Unlike Zombies and Skeletons, Creepers will not catch on fire in direct sunlight, meaning they can wonder around unharmed any time of the day until it is killed or despawns. However, the Creepers will still be agressive during the day.
Creepers spawn in the overworld at night and in locations with not a lot of lighting, just like regular hostile mobs. They are especially dangerous as they are most completly silent (exept for footsteps andtheir hissing noises when they're ready to explode.