Use arguments for drupal views 3
Arguments in Drupal 7 are the same as contextual filters. Contextual filters are associated with the path of the view (or the view's page). With these, we give a basic determining factor as to how we want to narrow down the view's output. It can be set up on what ever you want it to be. One of the simple ways to do it is by content type or user name. 
Check out this page it explains it well. http://drupaleasy.com/blogs/ultimike/2009/07/using-views-relationships-arguments-attachments.
I also found these vids while searching  on relationships and contextual filters (arguments). Check them out they put a lot of things in perspective and teach you how to use them both. 

Drupal 6:
http://gotdrupal.com/videos/drupal-views-relationships 
http://drewish.com/node/127

Drupal 7:
http://vimeo.com/22100751