A float object, or f, can store a number. Here it holds the current Counter value.
A Message with value 0, resets the counter whenever clicked in Execute Mode. There is a comment of Reset, next to the Message. The bang object will increment the Counter when clicked in Execute mode.
A Number is used to display the output of Counter, that is the f object. A + object is used to feed the output of f to the right input of f. The comment of Counter indicates the number displays the Counter.