Ranking
Go to your clan page @ http://forum.toribash.com/clan.php
Go under the members list and there is a 'invitations' section
You enter the players username in the box and press the invite button
The user then needs to go to the forums (where you posted this)
Go to the top right where it says 'private messages', but if they have a clan invite
will say 'notifications', apon clicking the notifications text it will open a menu
they will click 'clan invitations' and will be able to accept the invitation

also from what i know if they go to the clan page @ http://forum.toribash.com/clan.php
and are not in a clan, they can accept it there