What is an integrated circuit board? What's the use? What is the working principle?

The word "integrated circuit board" is wrong.

It can only be called an integrated circuit or a circuit board.

An integrated circuit integrates many components (such as resistors, triodes, diodes, etc.) by a special process.

Finally, it is encapsulated with resin.

The circuit board is the mounting carrier of various discrete components.

And it is connected by copper-coated wires.