I've recently started a digital electronics course with a lab component (so far not at all related to the lectures). Unfortunately, there are no prerequisites for the course and I guess they somehow expect us to know a whole lot about circuits, but I'm completely confused. I"ll just ask two questions now and maybe if I don't understand some other things we can clear those up as well. 1. How do circuits like these make sense? I thought you needed a closed loop to have current flow .... 2. This is an example of an "active high" circuit. "When a switch is closed, the signal will be connected to power. When a switch is open, the signal will be connected to ground through the resistor." Does this mean that when the switch is open, there is actually current flowing through the wires? I feel really stupid :(.