You can simply create a new layout for your splash screen, then set that layout to be the "First Layout" by clicking "view" next to project properties (in the properties window) and selecting the new layout. Then when someone clicks on the splash screen (or a timer ends, etc), have it run the action "go to layout," pointing to the first layout of the actual game.
If you're actually looking to make a custom layout that runs while the project loads, that's a "loader layout," and is handled differently https://www.scirra.com/tutorials/318/ho ... ng-screens