If you do not have a Pirate101 Membership and are playing your way through the game with Crowns, you will encounter Premium Areas as you move forward in quests. Premium Areas separate chapters into sections that you can purchase individually.
When you approach a Premium Area, a window will pop up and you’ll have the option to purchase access to a new area in the game with Crowns.
Once you buy access to an area with a Premium Area with Crowns, that access stays with the account you purchased it with. Even if you then get a Membership and let the Membership expire, areas bought with Crowns are forever available to your account.