mysql has nothing to do with apache, it's just another server. you have to tell the php script (or perl script etc.) about mysql (your username/password/path/port), apache doesn't need to know. so if you try to install the phpbb forum, there certainly is some file called install or configure.php or something where you have to insert info about your mysql database. read the readme.
also, of course you have to start the mysql server before you try to connect to it. have you started it? start the mysql daemon, it will start the mysql database automatically, and create a basic config file, which you should update afterwards (e.g. adding the innodb instructions etc.)
