Please explain the @Produces annotation in CDI

I have read about the @Produces annotation in CDI, but I don't understand its usage.

public class Resources {

// Expose an entity manager using the resource producer pattern
@SuppressWarnings("unused")
@PersistenceContext
@Produces
private EntityManager em;                                        // 

@Produces
Logger getLogger(InjectionPoint ip) {                            // 
    String category = ip.getMember()
                        .getDeclaringClass()
                        .getName();
    return Logger.getLogger(category);
}

@Produces
FacesContext getFacesContext() {                                 // 
    return FacesContext.getCurrentInstance();
}

}

taken from: http://www.jboss.org/jdf/quickstarts/jboss-as-quickstart/guide/GreeterQuickstart/#GreeterQuickstart-

How does the container know to call a producer method? If I inject an EntityManager, how does the container call the @produces EntityManager? And how would a getLogger producer method get called?

I also don't see the reason to go through all of the trouble.