You browse the admin pages using your web browser. part of the catalog tutorial is to create the Admin pages for insert / Update/ delete and the other part of the tutorial is to create the public pages to browse the catalog.
When running the data assist create pages wizard to create the admin pages, on the manage pages, you can go into the field settings panel to set the field types. In that panel, you can select to add file upload to certain fields when creating the admin pages.