ios – how progress bar works?

that is viewcontroller file

import UIKit
class ViewController: UIViewController {

@IBOutlet weak var ProgressLabel: UILabel!
@IBOutlet weak var progressBar: UIProgressView!
let progress = Progress(totalUnitCount: 10)
override func viewDidLoad() {
    tremendous.viewDidLoad()
}
@IBAction func StartCount(_ sender: Any) {
    // 1
    progressBar.progress = 0.0
    progress.completedUnitCount = 0
       // 2
       Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { (timer) in
           guard self.progress.isFinished == false else {
               timer.invalidate()
               return
           }
           // 3
           self.progress.completedUnitCount += 1
           self.progressBar.setProgress(Float(self.progress.fractionCompleted), animated: true)
           self.ProgressLabel.textual content = "(Int(self.progress.fractionCompleted * 100)) %"
    }
}

}

that is an instance of progress bar can some one make me perceive what’s the code