Using hook

Hello,

I’m very happy with your plugin and would like to use it in my hooks. The aim is when a user register, to be able to place him in a specific group automatically.
I’ve seen the shortcode [groups_join group=”X”] but would prefer to use a function instead of the shortcode (to apply as soon as the form is filled). Could you indicate me which function I need to use for this and how.
Many thanks
Pat

http://wordpress.org/plugins/groups/