If something pokes your hand, you will probably look at your hand to see if it pierced the skin. To pierce means to go right through, especially with something sharp.
Pierce has several meanings, but they all involve something sharp penetrating something else, like scissors through a plastic bag or a pen through a pocket. You can also pierce confusion by saying something that makes everything clear. Another meaning has to do with sound. Much like a knife, a sharp sound can pierce the silence and a loud, high shriek will pierce your ears.