im sorry, you may not like this answer, but you don't.
Start minecraft go to [single player] select [Create new world] name it change default landscape to super if wanted OR add or remove premade buildings (small villages) and villagers.
Use a world editor or get a premade one from the minecraft forums.
In most cases you can just generate a "Super-flat" world in the world gen options.
On the singleplayer option, click 'create new'. You will be able to customize it and set its name. When you are done click 'create world'.
You click "Create New World"
log in to minecraft, click singleplayer, click create new world, then choose what you want in it.
Click "Create new world" and name it. There ya go.
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.
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
When you create a new world, it uses a random seed, unless you specify which seed to use.