Hi Dalal,
IIRC, content for the static pages plugin is stored in the database, so you can't really use any PHP code in them (only HTML/javascript). You can create your own pages, but it would take a good deal of work and would require some familiarity with the system and definitely some PHP experience. To do this, I would suggest duplicating the 'about' directory in the pages/ and template/ directories, and renaming 'about' everywhere to the name of your new page (e.g. 'newStuff'). If you do this correctly you would then access your new pages through
www.yourdomain.com/ojs/index.php/newStuff/. This is of course a very high level description of what to do--Actually doing this entails a significant amount of work, especially if you're not too familiar with OJS.
Cheers,
Matt