I've got a couple of short questions about chmod/mkdir functions on PHP. I've been reading <http://php.net/manual/en/function.chmod.php> and got confused with chmod.

1. What is the meaning of second number(7) on chmod("...", 0700), as I
understand only owner can do stuff anything with the files, but what
exactly is this owner? I mean is it PHP script or is it me typing in
URL that exact file with its location?How does it even recognize
"owner"?
2. If for example I make a folder this way:

mkdir('user\_files/'.$logged\_username.'/', 0700);

and then I'd put some files in that $logged\_username folder, are the files removable by anyone?

Hope these questions even make sense...Thanks for your time.