php chmod mkdir

I want to know what is the safiest chmode for creating user folders and user files. I create a user folder for each registration (in mode 700) and users can upload images into their folder. I read the php documentation but I'm still confuse about terms "owner", "group",开发者_如何学编程 "public"? Can I have a full explanation about it? (I can't found a good explanation on google)

Thanks.

This description seems decent:

http://www.perlfect.com/articles/chmod.shtml