Sorry, apps are turned off. If you know who runs the server, tell them to enable apps.
In order to install an App from the App Store you must setup an isolated App Domain, this is because Apps from the store deploy to their own app domain and run under a separate process from your SharePoint sites. If your SharePoint site uses the DNS alias http://sharepoint.contoso.com you could have *.apps.contoso.com as your app domain.
1) Browse to Tenant Administration Site of the HH mode Site collection
2) Create App Catalog for Tenant by clicking on Manage App Catalog
Note – Every Tenant Admin will require a App Catalog(Make sure Self site creation is enabled in order for App Catalog to get created)
$Sub = Get-SPSiteSubscription http://hhmodeSite(This CMDlet will help in fetching the subscription ID of the HH mode site collection)
Set-SPAppSiteSubscriptionName -Name "Name for Subscription" -SiteSubscription $Sub
We need to run the above command in order to set the unique name for domain under which these apps will run.More details can be found under http://technet.microsoft.com/en-us/library/jj219503.aspx