iOS & Swift - How can I get and save a UIImage from the user?

I am writing a Swift app for iOS. I want to know how to get an image from the user's camera roll (or whatever they're calling it these days) and save it locally within the app so that I can reference it later. How would one go about this? As an example, let's say I want to get the image and set it as the image for a UIImageView in my storyboard.I am writing a Swift app for iOS. I want to kno