Portal 2 Map Editor (not to be confused with the in-game map editor) is an modification to the game Portal 2, it's sole purpose is to build maps in a simple and effective fashion. It's not supposed to be the best choice of Portal 2's mapping tools, but rather as an extra asset to the primary mapping tool which is of course, the Hammer Editor.
Q: HOW TO INSTALL?
A: OPEN ReadMe.TXT FILE
Q: HOW TO SAVE MY MAP?
A: OPEN MENU THEN SELECT Save Game
Q: HOW TO SAVE MY CO-OP MAP?
A: ACTUALLY YOU CANT Save... (This Will Be Fixed Later)