There are two ways that you can add Packages to your Catalog within the Package Explorer.
You can add a Packages "from scratch" via the New button. You can choose to create a Package, Allowance, Bundled Cable, or Solution - all of which are types of "packages" in SI. The links above will explain the fields for each type of Package.
You can copy an existing Package to create a new Package via the Clone feature.
You can select Products in the Product Explorer and use the Add Items To button to add them to a Package, Allowance, or Bundled Cable.
You can select Labor Items in the Product Explorer and use the Add Items To button to add them to a Package or Allowance.
You can create Packages within the Project Editor by selecting items and using the Add Selected Items To feature. The Packages will be Project-specific unless you decide to use the Update to Catalog feature.