Answer: A lot of students are able to make it into classes they have waitlisted, but it all depends on the popularity of the teacher and class. Be sure to have another class/teacher in mind as a back-up.
Once you are able to add the class, you will receive an email to your BYU-Idaho email notifying you. You will then have 24 hours to add the class, or you will be removed from the waitlist and have to re-add yourself to it.
A professor may adjust their cap number if they under anticipated the popularity of the class. However, if they do not adjust the number, you can reach out to the professor to see if they would still be willing/able to take extra students.
See How to add to Waitlist for more information.