im sorry, you may not like this answer, but you don't.
You click "Create New World"
log in to minecraft, click singleplayer, click create new world, then choose what you want in it.
Well, if you mean as in ''creative'' or ''survival'' they are right there once you click create new world. If you mean texture packs you can download them off of minecraft sites.
Click "Create new world" and name it. There ya go.
You create a world and go into the world in minecraft.
After you log in, select Single Player and select "Create New World" to get a new random map.
To generate a normal world in Minercaft. Go to the game menu, create a new world, and make sure the world type is on normal.
Click on start game then click on create new and it will say name world and under that it says world seed
You simply create a new account
You can delete the world and create it new one. Plus you can swim in Minecraft so I don't know why you would drown.
Its in the new update
You can make a custom map on minecraft with out a map editor by building or demolishing certain land features or you can use a seed by typing your seed in the bottom box on the "create new world" menu.