The barnacles have a symbiotic relationship with a whale because they stick to the whale to catch a ride and get food that comes there way and the whale is not harmed nor benefited.
Some small fish have a symbiotic relationship with larger fish because they will hide under the lager fish for protection. In the relationship the smaller fish gets a benefit and the larger fish is not benefited or harmed, therefor this would be called commensalism.
The mosquito has a symbiotic relationship with a human because it lands on it and benefits by sucking the humans blood. This would be considered parasitism because the mosquito is benefited but the human is harmed.
The bed bug has the same relationship with the human that the mosquito does but the bed bug eats human flesh instead of sucking blood. This would also be an example of parasitism.