title: What does subscribe do, and how it is related to Observable?
body: <p>I'm new to Angular and the tutorial I followed has the term "<code>Observable</code>". The tutor explained it, but I didn't completely understand.</p>
  
  <p>What is an <code>Observable</code>, and why do we always have to call  <code>observable.subscribe()</code>?</p>
  
  <p>What does <code>subscribe()</code> actually do?</p>