This is part 2, if you have not read part 1 then we would suggest you go back and do that now. We can wait. Right now you should have an image stuck to a board, but no way to erode that pesky exposed copper. Fear not, for we bring you the answers you seek. We will explain several methods of actually etching your board as well as the processes involved with each.
*EXTREME WARNING* Nearly all of the materials used in etching carry some sort of hazard, either to your respiratory system or any exposed appendages/skin. If your containers have warnings on them, please read and follow them. If no such warnings are present, good lucksurviving in a country with lax health and safety standards. You should always be wary when using chemicals and take the proper safety precautions.
Part two of the extreme warnings: time to bum you out even more. Acids are an environmental hazard. Dumping these chemicals into the water supply via the drain could create several potential problems (some of which you may not even see right away). There are proper methods of disposal which differ from country to country, so just check what you are required to do.
Some people prefer to instead opt to reclaim some of the materials, which is rewarding in its own ways. Back to the stock standard lecture: always work in a well ventilated area, always wear gloves and goggles, assume the glassware is trying to kill you, and all that.