It calls up the Finder, hides all other running applications and opens a Palette with my most important locations like the sidebar favourites in a Finder window.
The Palette entries were created to open the new window in a dedicated position on the screen.
I used to have a nicely formatted, searchable list of all KM Actions, Text-Tokens, and Functions in a BBEdit document (readily available via a keyboard shortcut).
I had an AppleScript that would harvest all that information from the Keyboard Maestro Editor's menus, and I had to update it when Keyboard Maestro's version got bumped.
But then Peter built the Insert-(Action, Token, Function, Variable)-By-Name capabilities into the Keyboard Maestro Editor.
So now when I'm looking for something I'm not familiar with I pop one of those up and start fishing.
When I know more or less what I'm looking for it's all that much easier.
These days I rarely use the Actions Inspector Panel in the Keyboard Maestro Editor (Actions > Show ActionsβK), but now and then its divided categories of actions come in handy.
I also have access to the Search Menu in the Keyboard Maestro Editor's Help Menu, and that occasionally gets me where I want to go a bit faster. (β§β?)
If I still can't find what I'm looking for then I move on to searching the Keyboard Maestro Wiki and the Keyboard Maestro Forum.