Welcome!
It is important to be enrolled in the brown scapular to receive Our Lady’s promise as you are wearing Her habit. Enrollment is done by having a priest read the prescribed prayer. At which time, the priest blesses you and the scapular. Please note that the blessing of the scapular carries over to all your future scapulars as they become tattered, broken, lost, etc.
In other words, once your scapular has been blessed during the enrollment, you need not have new scapulars blessed. You can if you want to, though. The scapular must be worn over the scapula (shoulder blades) and collar bone so that the “squares” fall to the front of you and behind you.
Regarding the consecration to Mother Mary: a priest is not required for the consecration, but you may want to inform a priest so that he may bless your “little chain” (should you choose to wear one as a reminder of your consecration). I highly recommend St. Louis de Montfort’s True Devotion to the Blessed Virgin Mary, also known as Total Consecration to Mary.
This website helps with all the requirements:
totalconsecration.ageofmary.com/index.html
Peace be with you.
+JMJ+