accessing and downloading on demand resources iOS9

I am trying to implement new iOS9 feature app thinning, I understood how tag an image and enable on demand resource in Xcode 7 but I don't understand how to implement NSBundleResourceRequest in my app, can someone help me, that would greatly appreciated

First, check if the resources are available. Else download them.

Here is the swift code I use

let tags = NSSet(array: ["tag1","tag2"])
let resourceRequest = NSBundleResourceRequest(tags: tags as! Set<String>)
resourceRequest.conditionallyBeginAccessingResourcesWithCompletionHandler {(resourcesAvailable: Bool) -> Void in
    if resourcesAvailable {
        // Do something with the resources
    } else {
        resourceRequest.beginAccessingResourcesWithCompletionHandler {(err: NSError?) -> Void in
            if let error = err {
                print("Error: \(error)")
            } else {
                // Do something with the resources
            }
        }
    }
}

I also found this guide very helpful.