Good day Ball22990929,
If you are planning on using a family membership in Apple Music, you should first set up your Family Sharing. See this article for how to do so - Set up Family Sharing.
Once Family Sharing has been set up, use this article to set up the family membership in Apple Music - Join Apple Music on your iPhone, iPad, iPod touch, Mac, or PC.
Thanks for using Apple Support Communities.
Safe computing.