You can add tabs using the Navigation Manager (Under the Settings menu in the admincp). There's a FAQ Manager (under FAQ) where you can create FAQ pages. There's already a link to the FAQ under the forum tab, but you could copy the url and use it for a tab. As for "About", I suppose you could create a CMS page of some type, or else create a custom page, maybe using this method:
https://vborg.vbsupport.ru/showthread.php?t=228112