First, it has to be able to make copies of itself because you're making new cells all the time and your cells have to have a copy of your DNA so it has to do what we call replication.
It also has to store all the information about your body as far as your body chemistry, your proteins, your amino acids, and all the things that make you.
One more very important job of DNA is that it's responsible for this process called protein synthesis which is the process in which cells make proteins. So every piece of your body from your fingernails, your eyeballs, and many other things are made up of proteins, proteins are the building blocks of you and the DNA determines the shape and function of your proteins. You think of DNA as a set of instructions on how to make the proteins that make you.