Click Memberships > Subscriptions/Packs > Subscriptions
Name it, price it, choose duration settings: 'absolute interval' for renewing subscriptions, 'specific interval' for fixed start and end dates.
At bottom of page choose whether certain classes will not be included and, below that, choose whether it will have 'auto - enrolls', where subscribers are automatically enrolled in certain classes.
Click Create, then choose whether to make it public by clicking Subscriptions/Packs > then turning on the 'Featured at Checkout' toggle.