If you're interested in creating apps, you'll need to learn Swift. Swift is a powerful and easy to use programming language for macOS, iOS, watchOS and tvOS. Apple created the Swift programming language in 2014. It's designed to be fast, safe and interactive. The syntax is concise yet expressive, and it includes modern features like type inference, closures, generics and multiple return values.
Learn more about Swift here: https://www.apple.com/swift/