Question about unknown concept

I don’t know what is it(circled thing on pic), and can somebody type me?

That is a UIAlertController.

How can I create UIAlertController messages without buttons?

A UIAlertController is a ViewController in which you need at least one button to dismiss it. Here is a generic function to show an Alert in which you pass a title and a message.

func showAlert(_ title: String, message: String, buttonText: String) {
        let ac = UIAlertController(title: title, message: message, preferredStyle: .alert)
        ac.addAction(UIAlertAction(title: buttonText, style: .default, handler: nil))
        present(ac, animated: true)

In this app was no any buttons built in app. Only I pushed on triangle, that launches a video in that site and then was displaying this message. Can you explain me why?

Can you provide a screen capture of the triangle you are referring to?

Circled triangle on the pic.

That’s just a play button similar to that used for YouTube videos and other Apps that display videos.

In that App you are using, tapping that play button must do something other than play the video. What is the name of the App you are using?

I don’t use it now. It’s video Saver.

How can I use this buttons?
And can you recommend me some materials about such buttons?