Searching in google by "unix permissions" you can get lots of information. For instance:
http://www.zzee.com/solutions/unix-permissions.shtml
Though, it seems that you have a problem of understanding the perms representation. The operating system just sees a bunch of bits, but human beings can represent them in several ways.
In general, when you write 755, 644, 400, etc... You are talking about user/group/others and representing those bits in octal. But, when you see something like 0700, 2755, 4755, etc, you are representing rwx perms plus sgid, suid, sticky, etc... Just have a look at the page above for examples.
Regards.