Symbiosis
Commensalism
A bird living in a tree. http://images.fineartamerica.com/images-medium/bird-in-a-tree-paul-sequence-ferguson.jpg
Commensalism is like a bird living in a tree. The bird benefits by having the tree to live in. The tree is not harmed by the bird living in it.
Mutualism
A bee pollinating a flower. http://sathiyam.tv/english/wp-content/uploads/2013/02/bee-flower-648.jpg
Mutualism is like a bee pollinating a flower, they both benefit from each other. By pollinating the flower, the bee gets food. When the bee pollinates the flower, it allows it to reproduce.
Parasitism
A tic on a human. http://img.webmd.com/dtmcms/live/webmd/consumer_assets/site_images/articles/health_tools/bad_bugs_slideshow/dermnet_photo_of_tick_burrowing_in_skin.jpg
An example of parasitism is a tic on an animal. The tic benefits from it by drinking the blood of the animal. While the tic gets what it wants, the other organism is being hurt because the tic is drinking their blood.