So you have a bunch of musical Sims and you want to do more than just Jam together? Then start a band! Work on those musical skills and relationships and get started. They need to know each other enough to be able to give the option of Ask to Form Band (it'll usually be in the Friendly tab) before you can do anything. Once it's formed then members can ask other sims to join. You'll get to name the band to and when you become good enough you'll be able to start getting gigs at local venues. Like in the Singer career you'll gain reputation and experience and climb the industry ladder!