title: What does "Changes not staged for commit" mean
body: <p>I thought if you want to track the files you should  <code>git add [files you want to track]</code></p>
  
  <p>I don't know why I got the messages <code>Changes not staged for commit</code>.</p>
  
  <p>If those files were not staged, shouldn't <code>git</code> shows me those files were  <code>Untracked</code> like that</p>
  
  <p><img src="https://i.stack.imgur.com/aQtQ0.png" alt="enter image description here"></p>
  
  <p>All I've done was create a new feature from <code>develop</code> branch and worked in <code>feature/change_excel_format</code> branch</p>
  
  <p>I thought Those files should be in <code>staged</code> status,</p>
  
  <p>But <code>git status</code> told me <code>Changes not staged for commit</code></p>
  
  <p><img src="https://i.stack.imgur.com/Zxl9h.png" alt="enter image description here"></p>
  
  <p>To brief, 
  I only know there are 3 stages in git  <code>untracked</code>, <code>staged</code>, <code>committed</code>
  Can any one tell me , what was the stage in for <code>Changes not staged for commit</code>
  <img src="https://i.stack.imgur.com/CEwGG.png" alt="enter image description here"></p>
  
  <p>So if I modified the  file <code>a</code>  (already in the repo)</p>
  
  <p>and type <code>git st</code> , the git will tell me <code>Changes not staged for commit</code></p>
  
  <p>if I  <code>git a</code> then the file <code>a</code> will be in <code>staged status</code></p>
  
  <p>if I modified the <code>file a</code> now, there will be two status of <code>file a</code> in <code>git</code>, right ?</p>
  
  <p>So I have to decide if make the <code>staged a</code> be commit or make the <code>not stage a</code> to be staged,
  and then the previous staged <code>file a</code>will be discard ?</p>
  
  <p><img src="https://i.stack.imgur.com/6kLX2.png" alt="enter image description here"></p>