Answer: Parasitism is when one organism gets harm and the other benefits. Commensalism is when one organism benefits from the other but the other does not benefit or receive harm. Mutualism is when both organisms benefit from each other.
Examples: Tick sucks the blood out of the dog which is bad for the dog but good for the tick= parasitism. Cleaner wrasse cleans the gills of fish and the fish gets clean gills and the wrasse gets food=mutualism. Remora on large marine animals gets the food scraps and the marine animal gets no harm and no benefit either=commensalism.