In the CatalogBrowser you select catalogs from the catalog database to open them in the PageBrowser.
The CatalogBrowser shows the content of the catalog database regardless of where the particular CDF catalog files are physically located. It is the quickest way not only to select a catalog but to also view a catalog's table of content with all chapters and page titles.
The CatalogBrowser not only shows the catalogs installed on your hard disk but can also show catalogs, which are logically installed in your system but which are physically store elsewhere such on CD-ROM or on a central catalog server accessible via Internet.
This is the CatalogBrowser form:

In the top part you see all the available catalogs while the table in the bottom contains the table of content of the currently selected catalog.