If you search how to build the logout text link for the Joomla! then you are at the right place now. The answer is below

<a href="index.php?option=com_user&task=logout">Logout</a>

Do you need to redirect user to the needed URL after logout? Then you have to add the parameter return=[your-base64-encoded-return-URL]. For example

<a href="index.php?option=com_user&task=logout&return=<?php echo $returnURL; ?>">Logout</a>


$returnURL = base64_encode('URL to redirect');

Or if you need to redirect to the site root of your Joomla! installation after logout then you can use this link with preencoded return parameter value

<a href="index.php?option=com_user&task=logout&return=Lw">Logout</a>