Scan to Catalog is one of many ways to add items to your Catalog. Scan to Catalog lets you add large and nested groups of photos from folders on your hard drives. 

Go to Catalog> Scan to Catalog

Optionally, you can choose to include or exclude file extensions. 

Exclude these extensions: All files other than the ones you list will be scanned. 

Include only these extensions: Only the file extensions you list will be scanned. 

Note: Use caution with the "include only" option. You must be explicit when listing file extensions, and some filetypes have multiple extensions, such as JPEG;JPG;JPE

Once a scan starts, you can start browsing right away, but only indexed photos will be available in searches. The number of photos visible will automatically increase as the indexing completes. 

Note: You won’t be able to scan items to a catalog if the Add checkmark is not selected. The items will be added to all catalogs with the Add checkmark selected.