The Default Lister is a special saved layout that consists of a single Lister. It is generally used whenever a "new" Lister is opened and a specific saved layout is not specified. The default Lister exists automatically - you do not need to create it yourself - and by default, it is updated automatically whenever you close a Lister.
There are many different ways that a new Lister can be opened, and whether the default Lister is used or not depends on the method you open the Lister and any settings that may affect that particular method.
If Opus was't already running the options on the Launching Opus / Startup Preferences page control whether the default Lister is used or not.
The default Lister isn't used whenever a saved Lister layout is opened - either by manually opening the layout, or by triggering an action (like double-click on the desktop) that's configured to open a layout.
The Default Lister Preferences page contains options that control how the default Lister is used. Three options are worth mentioning here: