Something is impaled if it has had something strong and pointed stuck into it, or even right through it. Something that is Impaled is usually supported above the ground by whatever it was impaled on. The monitor in the picture has been impaled on a post.
When a lot of something that you really don't want, comes to a place where you don't want them, they are infesting that place. You might have aphids infest your rose bushes. Infestations usually take some effort to get rid of.
You ingest something when you take it into your body, usually by eating it. Ingest is a more technical term for eating, but can also include non-food items that you have ingested that aren't actually edible.
Injecting is a way of forcing a liquid inside something else. Medicines are often injected into people's vein using a syringe. The person in the picture is injecting marinade under the skin of a chicken before cooking it.
You instruct someone when you tell them what to do in small, helpful steps. The man in the picture is instructing the woman. See also instructions.