There is little in basic electronics that cannot be explained with water.
A NPN BJT. Normally no water can flow from (C)ollector to (E)mitter with the (B)ase valve switched off or no water flowing into the B pipe. What does flow from C to E is leakage from the valve or C to E current leakage
Start injecting a little water into the Base pipe and it starts the C to E valve to open. The amount of water flowing out of the E pipe is B pipe amount + C pipe amount of water flow.
Too much water flowing into the B pipe causes the C to E flow to reach a maximum due to water pressure and pipe size . This is saturation. To much B flow will kill the valve. A base resistor acts as a pressure reducing valve reducing the flow of water into B to prevent damage. C and E flow also need a resistor to limit the flow to prevent too much flow causing damage.
The amount of gain is the tiny amount of flow in the B that causes a fixed amount of water to flow C to E. This is the DC gain of the BJT. How rapidly the valve between C & E responds to changes in flow into the B pipe is the AC gain of a transistor. Eventually the C to E valve will not be able to keep up with changes in the flow into the B pipe and the resulting flow will slow down and not respond. This is the bandwidth of the transistor coming into effect. Keep changing the amount flowing into B fast enough and the flow into B will eventually equal the C to E amount. The gain has become 1. Known as the transition frequency.
In N type MOSFETS it's much the same except it's the amount of water sitting behind a dam of the B (or (G)ate) stream and not the flow of water that causes flow from the (D)rain to (S)ource.
I have used N types as an example as this is easy to get into your head about what is happening. With P devices, it's much the same but upside down. Think about it.
Kirchoff's laws can be explained in exactly the same way.
Think of a current breaker. It trips if there is a current imbalance between live and neutral - i.e current flowing into the earth due to a fault.
If the water flowing into a radiator is more than the water flowing out of a radiator, then you have a leak in your radiator.
My old Polish teacher who struggled with his English explained this is how current works and from then we had a class of dozy 16 year olds fresh from school who understood how basic electricity worked within an hour and I will never forget this simple but basic analogy.