Databases are added to the database catalog when the database property "List in Database Catalog" is set. This can be found in the design tab of the database properties.
You may also wish to add a category such as Mail and this will be added to the entry when added to the catalog. There is a view in the catalog which allows you to view databases by category so it will save you some time looking for the databases you want.
The catalog task will run by default at 1am but if you want to run it adhoc you can use the command "load catalog" on the console.
Take a look here too: https://www.ibm.com/support/knowledgecenter/SSKTMJ_8.5.3/com.ibm.help.domino.admin85.doc/H_MANAGING_THE_DATABASE_CATALOG_OVERVIEW.html
Exporting the data is done by going to the view of choice and going to the File menu and selecting "Export...". I would suggest you try the .csv option as you can manipulate the data in Excel later. The view which you will want to export is Access Control Lists\By Application which has all the databases by file name.