title: What does the digit "1" mean when creating indexes in mongodb
body: <p>I am new to mongodb and want to make indexes for a specific collection. I have seen people use a digit "1" in front of the field name when they want to create an index. for example:</p>
  
  <pre><code>db.users.ensureIndex({user_name: 1})
  </code></pre>
  
  <p>now I want to know what does this digit mean and is it necessary to use it?</p>