CHMOD Permissions sets

U G W
rwx rwx rwx chmod 777 filename
rwx rwx r-x chmod 775 filename
rwx r-x r-x chmod 755 filename
rw- rw- r-- chmod 664 filename
rw- r-- r-- chmod 644 filename
U = User
G = Group
W = World
r = Readable
w = writable
x = executable
- = no permission

 
Here is another way of looking at it:
Permissions: 400     read by owner 040     read by group 004     read by anybody (other) 200     write by owner 020     write by group 002     write by anybody 100     execute by owner 010     execute by group 001     execute by anybody