Add an li class="TabbedPanelsTab" tag to the ul list of tabs, and a div class="TabbedPanelsContent" tag to the panel content container div tag. Do not forget to add the closing li and div tags when you add the code. For example:

<div class="TabbedPanels" id="TabbedPanels1">
	<ul class="TabbedPanelsTabGroup">
		<li class="TabbedPanelsTab">Tab 1</li> 
		<li class="TabbedPanelsTab">Tab 2</li> 
	</ul>
	<div class="TabbedPanelsContentGroup">
		<div class="TabbedPanelsContent">Tab 1 Content</div>
		<div class="TabbedPanelsContent">Tab 2 Content</div>
	</div>
</div>

You can add unlimited panels. For each TabbedPanelsTab li tag you must have exactly one TabbedPanelsContent div tag.