An etching is an intaglio print; the areas that hold the ink are below the surface of the plate. Other intaglio techniques include engraving, dry-point, aquatint and mezzotint.

The printmaker covers a metal plate with a waxy coating (the ground), draws an image in the ground with a sharp needle. The needle scrapes through the ground and exposes the metal, but the needle does not scrape into the plate. Wherever a line is drawn with the needle, there will be a line in the final print.
The plate is placed in a pan of dilute acid. The acid eats into the exposed metal and makes a groove. The acid resistant ground protects the other areas. The printmaker removes the pate from the acid when the grooves are deep enough. The ground is removed.
The printmaker covers the plate with thick, sticky ink, rubbing ink into all the grooves.
The printmaker wipes the surface of the plate clean, so only the ink in the grooves is left.
A sheet of damp paper is placed on top of the plate and padded with a blanket. They are rolled through the press. The paper picks up the ink in the grooves in the plate. When the paper is pulled away from the plate, the image has been printed on it in reverse.