HTML or XHTML Tags are what browser understand how to present data in specific tag like if you write something inside <h1></h1> browser have its default visibility how to show data inside these tags so browser have its default presentation for all xhtml tags. Anyway i will not describe or list all latest and old tags of html or xhtml , as i myself is a developer so not to make you bore i will list only tags which are used mostly so you can get only relevant information and not useless information.
Here are some xhtml or html tags below just for your understanding.
XHTML Document starts and ends with.
<h1></h1>,<h2></h2>,<h3></h3>,<h4></h4>,<h5></h5>.<h6></h6>
<p></p>
<strong></strong>
<ul></ul>, <li></li>
<ol></ol>,<li></li>
<form></form>,<input type=”” />,<textarea></textarea>.<select></select>.<option></option>
<img src=”” />
<a href=””></a>
<iframe src=””></iframe>
<table></table><tr></tr><td></td>
<div></div>
<span></span>
<br />
<hr />