So the etching method can be used for the production of printed circuit boards (PCB) since acid can be used to remove the unwanted copper from a copper clad.
A nice and easy method in order to make printed circuits at home is to use the so called : "toner transfer method". This method will be discussed in another article.
For now keep in mind that you have a copper clad (fr4) with the circuit "printed" (with toner) on it.
So this printed copper board can be etched with an acid solution called etchant.
This acid solution will eat all the unprotected toner and the remained, protected by the toner, copper will be our final printed circuit.