Click the green flag. Enter a value to set the green display to. (It's not actually a variable)
(I expected the display to be yellow, but it was green. What's up with that? Edit: Apparently the blocks were originally that color. https://en.scratch-wiki.info/wiki/Experimental_Blocks#Experimental_Control_Blocks_in_2.0) This uses the (counter) reporter that is not found in any menu. It can be set to 0 or increased by 1. It is a Control block, which is why I expected the display to be yellow. You can use this for anything you want.