FAQ:How can I create clothes?
Clothes are created with the MakeClothes tool, which is a part of the BlenderTools, see getting and installing BlenderTools .
The documentation on MakeClothes is a bit outdated, but can be found at Documentation:clothes.
There are also some useful tutorials that can be found from the documentation index.
Otherwise, following the video tutorials at Video:Blender_tools will probably be the best bet to get up to speed.