In SharePoint 2013, you can deploy the SharePoint Apps, either in a Private Catalog or the Microsoft SharePoint App Store or the both. A private Catalog is nothing but a site collection inside the SharePoint Web application. A tenant administrator can manage the app deployed in the private Catalog.
- Private Catalog
- Office App Store
The SharePoint Apps deployed in a private catalog can be made available to the entire site collection or the subset of the site collection. And the Apps published in the office app store can be purchased. Apps in the SharePoint App store can be downloaded from http://office.microsoft.com/en-in/store/apps-for-sharepoint-FX102825267.aspx