A Priest or Bishop is to do the blessing and enrollments into the scapulars.
Some scapulars are particular to certain religious orders such as the Black Scapular of the Seven Dolors of the Blessed Virgin (Servite)

and the Blue Scapular of the Immaculate Conception (Theatines) and can be very difficult to get except through them. For those types of Scapulars a special enrollment is needed by the order itself or by a Priest who has been granted that authority by the order.
For others such as the Brown Scapular of Our Lady of Mount Carmel, it is necessary to get it blessed by a Priest and go through an enrollment into the Scapular by a Priest who has the authority to do it. With the Brown Scapular any Priest has that ability The Blessing is usually conferred at the ame time as the enrollment. Many Parishes have this enrollment once or twice a year. You can also get a scapular, take it to the Priest, get it blessed and ask to be enolled…
Other scapulars require only that they be blessed by a Priest prior to wearing and have no special enrollment at all.
For those who have more than one devotion or can’t decide which scapular they want or just want to cover all the bases there is the five fold scapular which consists of five scapulars linked together. For this scapular any priest has the authority to enroll or invest the wearer.
Many scapulars come with indulgences attached but these all require that the wearer comply with certain rules for prayer and behavior peculiar to that scapular. Some don’t however and are merely devotional aids.
With most scapulars it is not necessary to have a new one blessed when an old one wears out. The blessing that was initially received will suffice as long as the wearer is in compliance with the norms of the particular scapular being worn…
With some scapulars when the original wears out it is acceptable to wear a medal which represents the scapular. With others it isn’t. When they become old and unwearable, you can either save them or dispose of them by burning or burying. ** DO NOT THROW AWAY IN THE TRASH**:tsktsk:
Also, the wool side is supposed to be worn next to the skin.
