chmod and chown

"chmod" changes the rights of a file.

"chown" changes the owner of a file.

In both cases, the file might be a directory as well.

Examples	Meaning
chmod u+x filename	user is allowed to execute filename
chmod u-x filename	user is disallowed to execute filename
chmod ug+rwx filename	user and group have all rights on filename
chown newowner filename	newowner becomes the new owner of filename
chgrp newgroup filename	newgroup becomes the new group for filename

For more information on possible flags, try man chmod, man chown.