You may try sth. like:
<a href="{$link->getCMSLink('8', 'new')|escape:'html'}">Your CMS Page</a>
inside you theme .tpl files.
Where:
'8' - CMS page ID
'new' - SEO "friendly" name
See: http://hassadee.com/2012/10/06/how-to-link-to-page-of-cms-in-prestashop/ and http://www.templatemonster.com/help/prestashop-1-6-x-how-to-add-cms-page-with-link-in-headerfooter-menu.html#gref for more info.