The Package Explorer is where you can add/edit/delete Packages in your SI Catalog. You can access this via the Start button->Catalog->Manage Packages:
There are three types of Packages in SI: Packages, Allowances, and Bundled Cable.
There are various buttons along the top ribbon of the interface:
Your Packages display in a grid. You can change what fields display in the grid via the Layouts section of the Home tab.
Here you can create and manage your Package Categories. Package Categories can help you organize your Packages: