CHMOD is a method for changing file and folder permissions on Linux based web servers.
If you are using a Windows web server, this method of setting file permissions does not apply to you. On Windows servers, file and folder permissions are usually automatically set for you based on the web hosts set-up, thus you should contact your web host regarding any permission issues you encounter on a Windows Server.
It is important to set the correct file and folder permissions to ensure the forum software can function properly while being as secure as possible.
Correct CHMOD Values
config.php: 666 before installation and 644 after installation
cache directory: 777
images/avatars/upload directory: 777
files directory: 777
store directory: 777
All other files: 644
All directories: 755
Using Your FTP Client to Set Permissions
You will need to connect to your web host using your FTP client. To do this, you will need the FTP client configured with your valid FTP login details. You may need to use your hosts FAQ or support to get these details.
Once you have connected to the host, you should (in most cases) be logged into the "root" directory. From here you need to browse down into the phpBB installation folder. It's location will depend on where you installed phpBB - it could be in the root or inside another folder.
Once you are in the right location, you need to right click a file, or highlight multiple files and then right click. In the right click menu select the option CHMOD/properties or something along these lines.
Note: Functionality will vary by FTP programs - not all programs are the same. What you have in the right click menu will depend on the FTP client you use.