Download the CSV template from the product library, fill it in and import it. Xero items and InteliOffice sales orders can also be added to a project.
In the web portal, open Products, choose Download Template, fill in the CSV with your products and use Import CSV. Tidy your category, manufacturer and supplier lists first so the imported products match them.
If Xero is connected, + Add from Xero on a project's Products tab adds items from your Xero catalogue to that project. If InteliOffice is connected, + Add from InteliOffice brings in the lines on a sales order, with their PO and SO numbers.
Products export too: the library and the Assets tab as CSV, and a project's products as CSV or Excel.