Redeem a code
A code gives you a term as a gift. It is not a discount and not a payment: nothing is charged, now or later, and there is nothing to cancel.
A code is added to an account, so you need one first. A Community account is free and asks for an email address and nothing else. Your code is kept and filled in again when you come back here.
Already have an account? Sign in and come back here.
Your code is redeemed.
What a code is
A code is a gift, not a purchase. No card was asked for, no payment was made, and there is no subscription behind it, so there is nothing to cancel and nothing will be charged when the term ends.
On the last day the products go back to their free Community plan and keep working there. You get an email a week before that happens.
A term you already paid for is not replaced. The gift is added on top of it, so no day you bought is lost.