Mutualism is a form of symbiosis where both organisms benefit from each other.
Commensalism is a form of symbiosis where one organism benefits and the organism is neither harmed nor helped.
parasitism is a form of symbiosis where one organism is helped and the other organism is harmed.
A mosquito and a human have a parasitic relationship - the mosquito benefits from the blood of a human, and the human is harmed.
A bee and a flower have a mutual realationship. The bee pollinates the plant, helping it reproduce, and the bee also gets nectar to feed itself
Barnacles and whales have a commensal relationship. The barnacles receive transportation which increases their food supply. Whales are neither harmed nor helped.