A profile is simply a record in Realm. Adding a person, organization or business to Realm means you give them a profile.
Any congregant, organization or business that your church has a connection with will likely have a profile. That means you can track data connected with them such as contact information. But having a profile doesn't mean they can necessarily log in to Realm. That requires an account, covered in another topic.
Where do the profile fields come from?
Families vs. Individuals
Every individual is related to a family in your database. A family can have one individual or many. If you're used to other church management tools that distinguish between the two, you should know that families are created automatically when you add individuals in Realm.