Okay kiddo, so a requiem mass is a special kind of church service that happens when someone has died. It's called "requiem" because that means "rest" in Latin, and it's a way for people to pray for the person who has passed away so that they may rest peacefully in heaven.
During the requiem mass, there's lots of singing and praying, and a special kind of music is played that is called "funeral music". This music is usually very slow and sad, because it helps people feel the sadness of losing someone they loved.
There's also something called the "liturgy of the word" that happens during the requiem mass, which is when someone reads from the Bible and talks about the life of the person who has died. This helps people remember all the good things about the person and helps them feel like the person isn't really gone forever.
So, that's what a requiem mass is all about. It's a special church service to help people remember and pray for someone who has passed away, so that they can rest peacefully in heaven.