XWiki classes question

Hello, I have the following question regarding relationing 2 classes in xwiki. I made a class Person with 2 properties (firstName, lastName) and a class Media with a prop. (title) and then I made an object "Richard Gere" of class person and 2 objects "Pretty Woman" and "Autumn at New York" of class Media. Now I would like to link somehow the 3 objects, i.e to say that Richard Gere played in "Pretty Woman" and also in the other movie (media). How can I do that? I don't seem to understand how to link the already created objects one with another. For instance, I cannot create another class with 2 properties, one of type Media and one of type Person, because these types don't appear under "Type" on "Add Property" panel. Please help me understand how can I do that in xwiki. Ps. I heard something about attachments but I don't really understand how... Thank you. Evelina Slatineanu