One method for adding Items to a Project within the Project Editor is to click either the [Add Products], [Add Labor], or [Add Packages] buttons in the ribbon of the Home tab:
The Add Products interface shown below:
Find what you are looking for via the Search field, Quick Filter, or column filters:
Use the quantity fields next to the Items to change the quantity if desired:
You can change the Price Type if you wish:
Select Location(s) and System for the Products.
Click [Add] or [Add and Close] to add the Item(s) to the Project.