This action can only be used within a loop action (for example, Repeat or While), and calling it will break out of the loop in that moment. Normally a loop will run either a fixed number of times or until a specific condition is met, but you can use the Break action to prematurely end a loop at any moment (actions within the loop after the Break will not be run).
The above action block code performs a Repeat loop 1000 times. In the loop it checks to see if a List data structure is empty and if it is not it removes an item from the list, and if it is it breaks the loop.