How does the arithmetic logic unit actually works?

问题:

In other words, how can energy combined with metal perform logic operations? In the research I've done i'ts always assumed how the 'magic' happens but usually there's a lack of explanation on how can a physical device can 'understand' and perform processes of logical nature. I think would be a good approach to first understand very simple devices as a calculator, but even with that I cannot grasp (and feel absolutely amazed)on how can a circuit be designed in such a fashion that it can perform 'thinking' activities. Thanks!