"I have a question about symbiotic relationships. I would like to know more about mutualism, commensalism, parasitism. How does each one happen? Thank you!"
it looks like you are pretty much involved in Ecology. As you probably symbiosis is the term applied to the relationship between two or more organisms.
When both benefit for the relationship it is called Mutualism. A Lichen is an example. Tick birds and termites are also examples
When one symbiont benefits and the other gains no benefit it is called Commensalism. The Remora fish is an example
If one symbiont is robbing the other of energy or causing harm it is Parasitism