Can someone help me understand clomid❓

Morgan • Nurse💉 wife💑 dog mom🐾 PCOS🤦🏻‍♀️ BOY MOM💙 #2 due 6/22

I was told to take it period days 1-6. And then get progesterone levels drawn on day 21. I’m assuming that means cycle day 21? They didn’t really explain but I always love to hear from my ladies on here!!