title: How to use NERD Commenter for vim -- how to use <Leader> key
body: <p>I found the NERD comment plugin for vim, but I don't understand the documentation.  Say I want to comment some code in c/c++ e.g.  </p>
  
  <pre><code>code line 1  
  code line 2
  </code></pre>
  
  <p>becomes</p>
  
  <pre><code>/*
  code line 1  
  code line 2  
  */ 
  </code></pre>
  
  <p>I have seen other threads on this, but to be honest I don't know what <code>&lt;leader&gt;</code> is in the <a href="http://www.vim.org/scripts/script.php?script_id=1218" rel="noreferrer">NERD commenter documentation</a>. When I try the accepted answer in this <a href="https://stackoverflow.com/questions/1375031/nerd-commenter-how-to-comment-out-a-range">other thread</a>, I end up executing the change command on the selected lines.  What is <code>&lt;leader&gt;</code> and, step-by-step, how do I go about commenting lines with <code>/* */</code>? </p>