I have had many people enquire what chmod 664 or chmod 750 means and it is really quite simple. The command will allow you to set the permissions for the owner/group/others of a file or folder.
The numbers 1-7 are made up of 4-2-1 and 0.
If for instance you run ls -al to see what permissions a file/folder has in terminal you dont see 750 you will instead see something similiar to:
drwxr-xr-x 2 ben ben 4096 Mar 26 19:46 Desktop
Looking at that we can see that its a directory because of the ‘d’ in drwxr-xr-x and that the owner (ben) has rwx (read/write/execute), the group (ben) has r-x (read/execute) and others have r-x (read/execute). Which relates to 755.
If we only want the owner (ben) to have access we can of course use chmod 700 Desktop