newbie: unix/php/mySQL permissions

I'm very new to php & mySQL and need some help understanding how I should set up my Unix permissions. I would like to run php code that could delete/create/edit existing files. I've tried to issue the load data infile statement from the command line but mySQL gives me a permissions error. How can I setup unix/apache/php/mySQL to allow for creation/deletion of files, but still be relatively secure against malicious code? Is there a permissions primer out there that could help this Newbie get familiar with how this all works? Thanks! -Bob