Lobby script is responsible for all the interaction in the lobby. The script enables you to customize UI elements and components of the game.
In the Characters tab, there are prefabs of the characters, as well as their images, which will be visible in the game menu.
In the Levels you should add your multiplayer scenes and the buttons that correspond to them. And then press the [Add to Build Settings] button, and the scenes will be added to the Build Settings.
UI Elements are the all ui objects in the Lobby scene, you can adjust them as you need.