Brushing baby’s teeth

My 1 year old is so frustrating when it comes to brushing teeth. He likes it and he doesn’t mind the tooth brush, but he doesn’t understand the purpose. So he ends up biting the tooth brush and sucking the tooth paste off and when I try to actually brush he gets confused...

I am trying to give it time but it’s only getting worse and his teeth are getting a little yellow so I’m really trying to get him to listen