Consider the circuit shown...
If the pushbutton switch S1 is open, the transistor is closed. If you close S1, a small current flows into the base and the transistor switches through.
The resistor R4 forms a loop with the transistor and the voltage across R4 is equal to the voltage across the transistor.
Knowing the behaviour of the transistor, ie its current-voltage characteristic, you can state for the Kirchhoff's laws...
You can analyze any circuit with Kirchhoff's laws, if you know the current-voltage (IV) characteristics of the components!
Kirchhoff's laws are essential for the development of integrated circuits containing millions of transistors. With the IV-characteristics of the components, the circuits are analyzed using Kirchhoff's laws before they are actually built.
But how do you analyze circuits with Kirchhoff's laws...?