Congratulations on getting a FIRST promo code! Here's how to apply that to your account.
First you'll want to select your membership tier. You can choose either FIRST or FIRST+
Enter your code at the bottom where it says "Your Code". See where it also says "Billed every month starting 9/21/2020, after your 7-day trial period"? Remember that date!
After clicking apply, you'll see that the trial coupon has been applied, and now it says you'll be billed on September 28, 2020 after your coupon trial period! Click submit and you're ready to start being a FIRST member!