file system function in PHP changes the file or folder permissions on a target file path. This function takes two parameters, first the target path and the second is the mode you wish to change the permissions to.
<?phpHOT TIP FROM ADAM:
$file = "public_html/myFile";
Using Filezilla you can get a solid direct reference of various modes you can set using numeric codes that make files and folders behave in different ways. I would write them all here but I am lazy and you can just go look for yourself.
1. In Filezilla connect to your server. Right click any file or folder on the right side(server side).
2. Click "File Attributes" and chmod your little face off. It will teach you what settings do what while you select and deselect check boxes in that window.
Download and use FileZilla... it is free and used to FTP files to your site from your machine. I use it religiously.