title: What is subscribe/@Output/@input in event emitter?
body: <p>I am new to Angular2 and I'd like to know what are:</p>
  
  <ol>
  <li>Subscribe</li>
  <li>@Output</li>
  <li>@input</li>
  </ol>
  
  <p>In event emitter in Angular2? And how I can use them in Angular?</p>