Look at the documentation for "chmod".
In a shell (command prompt) type:
"chmod" changes file mode bits, or permissions.
If you type:
this will change mode (permission) for g (group) and o (others)
by removing (this is the -) r (read) w (write) x(execute).
This leaves only u (user) with read, write and execute permission.
After you do this, if you decide you want to give everyone read permission, you could type:
and then g (group) and o (others) would get (this is the +) r (read) permission.