Can be found in "Settings" page.
Make database completion easier if you already used other software to write something to exif or iptc sections of jpeg or tiff files (only these formats are supported). Select a jpg file with metadata and click "list all tags for current file". You will see the list of available tags. Use copy and paste to add needed tags to the list in the main window, one tag per line. Since now, when you click right button in any field in the "Edit" page, you'll see a pop-up menu with your favorite tags. Select a tag and its value will be inserted to the field. In batch processes, use tags from "SHORTCUTS" submenu.