Open the App Catalog in you SharePoint environment. If you don't know the URL, follow these steps:
After you've done so - open the library "Apps for SharePoint" within the App Catalog.
Upload the app "TemplateHub.app" in the AppCatalog.
Now it is important to install the App within the App Catalog, this step is needed in order to assign required permissions. Choose "Site Contents" - "Add an App":
Click on TemplateHub and wait until the Installation is completed.