I am a beginner in electronics and I have two questions I hope you can help me.

1- I have studied and learned Ohm law, circuit analysis, circuit reduction and Kirchhoff's laws. I want to know whether circuit analysis methods and Kirchhoff's laws are used in detecting faults, or in the circuit design stage, and how this is done.

2- In all the content I have studied so far, all the problems and exercises are applied to circuits made up of only resistors. I want to know that in the case of real circuits, which contain other electronic components, how they are dealt with in terms of applying Ohm's law or Kirchhoff's laws. What I mean is that in circuits that contain only resistors, we can do all the calculations because the values of the resistors are known to us, but in circuits that contain other components with resistors, how can we know the value of the resistance of those components in order to perform the calculations.

3- In the design phase of any new circuit, we first put all the components of the circuit and connect them with each other, and then calculate the voltages and currents needed for those components? Or do we put the circuit components one by one and calculate the voltages and currents for each component?

Many thanks for Help..

Walid