The NOT gate has 1 input (In) and 1 output (Out).
The input can be 0 or 1, and the users can change (0 to 1 or 1 to 0) the value, with a click on the small box of the input.
The output (Out) has connected a red led to signal if the output is 1 or 0 (1 is red led, 0 is led without color).