LED
Shows one bit: lit for 1, dark for 0. Use it to watch an output.
Pins
One input on the left.
How to use it
Double-click to name it (S, C…) and it becomes an output column in the truth table.
Usage example
Wire the signal you want to watch into the LED: lit for 1, dark for 0. Give the LED a name (like Y) and the truth table and expressions will use it.
Common mistakes
An input pin takes only one wire — use one LED per signal you want to watch.