The secret is the Boolean algebra. It is the basis of all digital circuits and computer chips. With the following experiments you get to know the Boolean variables, operations and the set of rules and you experience it using logic circuits.
The set of rules is, in fact, very simple, but powerful. With help of these rules you can reduce and simplify complex logical problems until you are able to build the actual circuits. In this way you can develop adders, comparators and decoder.
Before you can start with the first experiments, make a few preparations.