If it is low enough, the switch is turned off. The transistor switches are connected inside the chips so that they perform logic functions. Once we learn the logic functions they perform, we can build devices without considering how the switches were hooked up to actually perform that function. In this course you will learn about both combinational digital logic and sequential digital logic. Both produce an output based on certain values of inputs.
Combinational logic uses only the present values of the inputs.
Sequential logic contains some memory. It remembers something about the previous inputs and reacts to the current ones accordingly. You are expected to read the book and come to class prepared to ask questions. You are expected to keep up with the homework each day. The final grade that you receive will be based upon your exam grades, homework grades, and design problems.