chmod Parameters

 drwxrwxrwx  1 username    users    2525 Feb 18 09:17 index.htm
  ^ / / /          /       /
  | V  V  V      ''|'''      '|'
  | |  |  |        |          `-- group the file belongs to
  | |  |  |        `-- user who owns the file
  | |  |  |
  | |  |  `-- others (users who are neither you or in the group)
  | |  `-- group (people in the group)
  | `-- user (you)
  |
  `-- d=directory, -=file, l=link, etc

Number Codes

0  =  ---  =  no access
1  =  --x  =  execute
2  =  -w-  =  write
3  =  -wx  =  write and execute
4  =  r--  =  read
5  =  r-x  =  read and execute
6  =  rw-  =  read and write
7  =  rwx  =  read write execute (full access)