A butterfly hovers around a bright colored flower because of its color and odor. It also sips nectar from the flower. This is Mutualism, so both the butterfly and flower benefit.
Commenalism is whenever one speices recieve a benefit but the other does not. For example, when small fish clean off bigger fish. It just benefits the bigger organism.
Parasitism is whenever one speices recieves a benefit and the other is harmed, like when animals eat eachother for food.