How do I associate multiple nodes to a user?
There is a module for handling relationships between entities for Drupal 7 which shows great promise called relation. At the current time it's still in alpha and I haven't tested it out for a while, so I am not sure where it is at. When I last tried it out, it wasn't quite suitable.

A more stable version which could be made obsolete by the relation module is the references module, which is a port of the Drupal 6 CCK node reference field. I've used that with great success.