Symbiosis refers to any type of close and long-term biological interaction between two different biological organisms. It's like two best friends who do everything together - they're always interacting in some way or another!
Commensalism is an association between two organisms where one benefits without affecting the other negatively or positively. Imagine if one friend has leftover food after dinner and gives it to the other friend. The friend who gets the food benefits, but the one who gave it away isn't affected because they were going to throw it out anyway.
Parasitism is a relationship between two species where one benefits at the expense of the other. It's like a friendship where one person always takes and never gives back - they benefit, but their friend suffers as a result.