The Groups Loop - per_page optional

@Tammie, how would I implement "The number of groups to display on a page before they are paginated to the next page. "

I have looked at the groups loop but don't know where I would add "per_page" in the code. If you could just advise me to where it should go and how it should look would be awesome.

link to the groups loop: http://codex.buddypress.org/developer-docs/custom-buddypress-loops/the-groups-loop/