The Palette contains all the modeling tools and is designed as the standard user interface that you will see on any installation of Alias.
The Shelf is designed to be customized by each individual user to suit their preferred way of working. Tools from the Palette can be dragged onto the shelf and arranged in tabs. Experienced users will build up their own customized Shelf over many months, and eventually it may replace the Palette altogether in their workflow.
The Shelf that appears when you first open Alias does not have any tools on it.