Use /generate to create a new world. In the configuration, you can configure the commands that will be run on your behalf when creating this world. Also, you can configure the creation of a pillar at zero coordinates, and other things. If you don't like this world, use /generate again. Seeds are saved in saves.yml. This can also be disabled.
Worlds are not deleted!
Do not name your main world with a number (worldname: 1). This can cause problems.