Build a template... for now a header.php with the page header. Include that in the page you would like to display it in. If you change the header.php file, everything that has included the php file will show that update. Now, that will handle basic updates of the header, for a fully interactive website you will need a database. The database will store essential information, and you will have to use PHP to query it. There is TONS of information about using php with mysql, so I will stop there.