New Subscriptions
Once prices have been set for the subscription period, go to https://squaresdb.mit.edu/gate/new_period/. Enter the first and last dance dates. Select the relevant season. Time should be correct (assuming the club dance time hasn't changed), and name and slug should populate automatically. Change the default price scheme to "normal", and fill in the subscription prices. Hit create (don't check "confirm"). Confirm the dates look right, check "confirm", and hit create again. That should be everything in SquaresDB to create the period. Don't forget to also update Squares Pay with the new period, though.
Shortly before the period starts, you'll want to import the payments. The Squares Pay page has more on how to do that.