The answer depends on your culture and belief system.
Scientifically speaking, our world was created when a planet, or star, exploded and the pieces fell into orbit around our current sun. Through thousands of years of evolution and climate changes, man finally surfaced and has been evolving since.
If you are of the Christian/Jewish/Muslim faith however, then the world was created by God (also known in the scriptures as Yahweh) and after a short time he created man, and woman, as his children and in his image.
If you reach further back than that - the Greeks believed the world was created by Chaos who gave birth to Gaea (earth) and she gives birth to Uranus (sky). Their children (the Titans and cyclops) begin a war that Zeus wins and he sends a flood to destroy the world with only one woman and man (Gaea and Uranus) surviving. When the floods end, Gaea and Uranus throw stones over their shoulders and create man.
There is also the Norse version which cites Niflheim as giving rise to 12 rivers which eventually produce Ymir, a giant cow, that licks a stone and creates man. This man, Bor, has three sons and they go on to create man out of tree logs.
And then there is the Hopi Native American version which has the creator, Taiowa, instructing his nephew Sotuknang, to establish nine universes (pretty interesting if you think up until recently there were 9 planets in the solar system and the Native Americans were big into the sky and the stars). Sotuknang creates Spider Woman who creates everything ,including man, from there.
Which one is the true creation story? It's not that black and white. Although science lays claim to it being the most factual, it can't explain everything and that's what creation stories are trying to accomplish. They aren't merely explaining how the mountains came to be or how man came to be, they are explaining how human traits came to be; good, evil, pain and suffering. As for who created the world..it's a lot like the question 'How many licks does it take to get to the tootsie roll center of the Tootsie Pop?' The world may never know.