I have basic understanding of chmod and CentOS file permissions. 777 stands for 111111111 and rwx for each root, group, user, etc. What I can't get my head around is setting up Apache, FTP and PHP to all work together correctly.

I have a proFTPd server and Apache server. How should I setup the permissions on the proFTPd server so that Apache server can read and execute the PHP files? On my initial setup, the files uploaded by FTP cannot be read by Apache. Should I put the FTP user and the apache server into a group?

How does the permission system work (FTP-Apache-PHP) on standard hosting systems?