The Main menu is the starting screen of Project Spark once the game has loaded and the Intro Video has been played (or skipped).
Here, there are two main options to choose from:
Play: play an Episodic Adventure—either Champions Quest Episode 1: Void Storm or Conker's Big Reunion—or create you own adventure in Crossroads.
Create: create new worlds via World Wizard or from Scratch, or edit and play worlds you already own. You can also go through the in-game tutorials to learn how basic game creation works inside Project Spark.
The aforementioned tutorials are directly available from the Main menu screen via the banner, which used to display the most recent content packs or show the latest news when the game was online.
Pressing Escape on the keyboard or Menu/Start on the controller opens the Options menu for global settings and game credits.
Since the services are offline, only your Gamertag is shown on your profile in the top right corner, and access to further profile information is impossible.