Working in a file with an HTML extension places Emacs in html major mode.

<p><pre>C-c 2</pre> Header 2 tag</p>

<p>
  <pre>C-c / </pre> Closes a tag
</p>

<p>
  <pre>C-h m</pre> Displays help / key bindings for major mode.  
</p>

<p><pre>C-c RETURN</pre> for a paragraph tag</p>