Okay kiddo, so there is a big group of people called Catholics who believe in a lot of things about God, Jesus, and how we should live our lives. Dogmatic theology is when they study and explain those beliefs in a really serious way.
It's like when you want to learn how to play a really difficult game, you read the instructions really carefully and try to understand all the rules. Catholics do that with their beliefs.
They use a lot of big words and concepts, but basically they believe that God is three people in one (the Father, the Son, and the Holy Spirit), Jesus died to save us from our sins, and we have to be really good and follow certain rules to get into heaven.
Dogmatic theology is important to Catholics because they believe that their beliefs are right and they want to explain them to other people. They also want to make sure that everyone who believes the same things is on the same page and not making up their own rules.
So, just like you study hard to learn how to play a game, Catholics study hard to learn and explain their beliefs. Does that make sense, kiddo?