A renaming action is simply a way of describing what you want the new file names to be.
A simple renaming action such as “Convert to uppercase” will simply take the current file name and make it uppercase, e.g.
Current Name -> CURRENT NAMEA Better Finder Rename offers a wide variety of renaming actions, organized into categories.
You select a category of renaming actions by making a selection in the Category: popup menu.
You select an action, by selecting an item in the Action: popup menu.
When you select a new action, a new set of controls appear below the Action: menu.
You can fine tune your settings by adjusting the values in those controls.