title: When are symbols used in Rails?
body: <p>I assume alot of these are built in or convetions, but methods like belongs_to or require uses a symbol for the model name it takes as an argument. </p>
  
  <p>And when it comes to methods like before_action, I'm not sure why there is a symbol in front of the controller actions as in the brackets below.</p>
  
  <pre><code>before_action :find_course, only: [:show, :edit, :update, :destroy]
  </code></pre>
  
  <p>Are all of these symbols used as a key of a hash or do most methods take symbols as its arguments?</p>