Instructions:
To build a circuit, click on the plus button. Then the library shows up and you can drag and drop symbols on the stage.
There are 6 logic gates, a clock, an input switch and an output symbol. To scroll down the library, use the mouse wheel.
To connect two symbols, click on an output and then on an input. You can drag symbols, as well as the stage. Use ctrl-click to delete objects and cancel wires.