Etching is one of the oldest printmaking techniques. First usually zinc, copper or metal plate needs to be covered with waxy ground which is resistant to acid. Afterwards an artist needs to scratch off an image using for instance engraving tools, any pointed tools. The point is that the artist needs to remove a wax layer where he wants a drawing to appear.
Then the plate needs to be taken out, washed with water, dried and it is a time to remove wax. After the wax is removed the plate is to be covered with printing ink or paint. The plate together with a sheet of paper is to be placed in a printing press in order to print the image.
I would recommend to see etchings by Rembrandt van Rijn (1606-1669), Gustave Dore (1832-1883), Francisco de Goya (1746-1828) in order to see what it looks like.