After you have set up your dependencies, you can view dependency lines in the Map view, as long as the devices appear in the same group. If the devices are not in the same group, you can refer to the Polling section of Device Properties to view the dependencies.
In the example above, the devices have an up dependency on the router, and the router has a down dependency on the hub. If the router's active monitors fail, the hub would be polled, and the devices behind the router would not be polled. When the router's active monitors are successful, the hub is not polled, but the devices behind the router are.