You've entered Crystaldimension! Yay! It's a world with characters from Hyperdimension Neptunia, Touhou and Di-Gi-Charat.
If you want to know which characters there are then take a look at Charas.
Or go to Gamindustri, Gensokyo or Akihabara.
On the Game page you can play an RPGMaker game which has the same characters.
The Theater is a place where characters interact or talk to the reader. It's like cutscenes from a visual novel but implemented in HTML.
Extra shows you images from anime and games I like.