Valve explains that the Portal 2 Authoring Tools include "versions of the same tools we used to make Portal 2." They'll let you create single-player and co-op maps, character skins, 3D models, sound effects, and music. PC Portaleers can find the Authoring Tools to download in, aptly, the 'Tools' section of their Steam library.
Here's what you'll find in the mod tools, if you want to get technical:
- Updated version of Hammer, the Source level editor
- Updated Faceposer
- Example maps and instances to help build new maps
- Updated suite of command-line compiling utilities