You can add custom static pages in Blesta by following this guide by a fellow customer of Blesta: https://www.blesta.com/forums/index.php?/topic/2943-blesta-32-351-how-to-make-static-pages-by-modifying-portal-plugin/&tab=comments#comment-21068
Or you can make life easier and use our BlestaCMS, our plugin makes life easier for you: https://blesta.store/cms