The buttons in the New section of the ribbon of the Project Editor allow you to add Products or Labor Items that do not exist in your Catalog. You can also add Misc. Items to a Project, click here for details on Misc. Items.
When you click either the [Product] or [Labor] buttons, a form will open that will allow you to create a new Product or Labor Item.
When you add a new Product or a Labor Item in a Project, it does not exist in your Catalog. If you wish to add the new item to your Catalog, use the Update To Catalog feature:
Also, if you wish to be prompted to update to the Catalog when you add new items within a Project or edit items within a Project, there is a Project Setting for this: