title: Back button on action bar
body: <p>when I create a new activity, Android Studio show me this photo:</p>
  <p><a href="https://i.stack.imgur.com/DQT47.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/DQT47.jpg" alt="enter image description here" /></a></p>
  <p>It have a Back button but activity haven't it. how can I Make visible it?</p>