Hello. chmod means "change mode". It sets a permission in UNIX which tells the server what the file is allowed to do. For example, perhaps you have a CGI program which needs to write information to file.txt. file.txt has no permissions to begin with, so the program will not be allowed to open it, and then write to it. If you set 'chmod 666 file.txt', it now has the permission to be written to. You also need to set permissions on cgi programs to tell them they are allowed to be run by people viewing them on the web.
I have to be able to CHMOD one directory to 777, whilst some files are at 775 and others at 666. I was wondering, how could I do this, I assume it has something to do with ticking/unticking the appropriate boxes.
Each of those 3 boxes has a value...the top box equals "4", the middle box is "2", and the bottom is "1"...so therefore, if you check all three boxes in the "owner" set, then you have a value of "7"...check all 3 in the other two sets, and you have two more 7s...total: "777".
755 would be all three checked in the first, and the top and bottom boxes checked in the 2nd and 3rd sets.