I have made a free program that uses GPL V3.0. It uses some art that is also under the GPL. What do I include in my software to be able to use the art

You can use the software and art on the same terms if they are available to you under the same license. You then license them to others on those terms. The entire purpose of the GPL is to make sure that you do not restrict downstream users from acquiring the same rights that you are employing. You simply include a reference to the GPL in your software and indicate that it applies to both the software and the incorporated art.