How to add custom data? [Swift]

I'm not exactly sure what you mean but I'll try to answer in multiple ways. First the "spinning logo gif". Do you mean the activity indicator to show loading? If so, it's similar to a button - you can drop it onto a view controller of your choosing and connect it with an IBOutlet or programmatically create it.

If you mean assets, like a picture of your logo for instance, you can create them in the size needed (remember to take into account @2x and @3x sizes - if its a 100x100 size needed, you create it as 300x300 and I generally drop it into Asset Catalog Creator), copy them into your Assets folder and use them in your storyboards or programmatically with something like UIImage(named: "yourImageName"). If you wanted to pull a picture from a URL instead (let's say you're hosting your assets online in Cloudinary or AWS), you can direct a URL with something like this:

  let imageURL = NSURL(string: "http://www.yourURLString.com")
  downloadImage(imageURL!, imageView: yourImageView)

 func downloadImage(url: NSURL, imageView: UIImageView){
        getDataFromUrl(url) { (data, response, error)  in
            dispatch_async(dispatch_get_main_queue()) { () -> Void in
                guard let data = data where error == nil else { return }
                imageView.image = UIImage(data: data)
            }
        }
    }

Is that what you mean?