I am a little confused because you say change file permissions and then at teh
end talk about a disk.

It is easy to change permissions for files in your home directory in Nautilus by
just right clicking on the file and choosing Properties and going to the
Permissions tab. Then you check or uncheck boxes.

If you don't have permission because it requires root access, then use sudo
nautilus or gksu nautilus (if you have gksu installed) from the terminal. Once
you provide your password, you should be in business.

The CLI way is to use chown . Use the manpages to find the exact syntax and
switches. For those new to Linux who want to learn the terminal (commandline
interface=CLI), the manpages are available to you from a terminal or in Firefox.
Type: man chown (for example). Also you can use the command --help like this:
chown --help. To exit the manpage in a terminal, just press q for quit.

In Firefox you type man chown where you would ordinarily type the url.

If you are not using Compiz then you can use ALT+F2 to bring up the run dialog
box, for typing in a single command. Compiz uses this key combination so you
will have to assign another key for this by going to System, Preferences,
Keyboard Shortcuts, if you use Compiz.

For drive permissions you need to edit etc/fstab, making sure that the drive
that you want to change is listed and then you need to change it as described
here:
http://ubuntuforums.org/showthread.php?t=283131