if you met your $5000 minimum spending requirement...

your 5 FN certificates should have automatically been deposited into your Marriot account (not your credit card account).

log in to your Marriot.com account, you should able to see your 5 FN certificates posted there.

when you book, you can attach your FN certificates to your booking, Marriot now allows you to book any hotel room for the maximum points allowed + 15,000 points, so technically speaking you can choose any room that is up to 65,000 points per night.