The alimentary canal is used when food enters the body and solid wastes are expelled out. So, when you eat or drink something the alimentary canal brings in down through it's canal and your digestive system "digests it", which then causes the alimentary canal to let solid wastes be brought out. The alimentary canal consists of the mouth, pharynx, esophagus, stomach, small and large intestine, and the anus.
Hope that makes sense...
