The “Perpetual Testing Initiative” DLC will allow players to create, share, and play puzzles with an in-game editor.
The Initiative comes with a simplified puzzle maker that allows that creation of mind-bending puzzles without ever leaving the game.
The puzzle maker can directly publish maps to the Steam Workshop where users can browse, vote on, and select to play them.
Valve also stated that selected puzzles will be automatically downloaded and installed within Portal 2. That sounds pretty awesome to me.
For more info on Portal 2 and its downloadable content, you can visit thinkwithportals.com.