Opening a database is just like opening a file in any other application. There is a "recently opened databases list" in a history in the Main Menu as well as the Main Toolbar, so you don't need to keep using the open dialog. doogiePIM also will automatically open the last database you had open in the previous session.
To Open An Existing Database
From the main menu, choose "File/Open Database", or
Choose from the recent open history available as a submenu, or
Click on the main toolbar icon "Open Database".
Introduction to Database Files
Creating New Database Files
Repairing and Optimizing Database Files