A hub is a query server that is able to integrate data across any data providers that it links to. In general, hubs will be configured to retrieve data from a few public data providers, but you may be interested in linking your hub to a new data provider, which could be either public or private.
To do this, visit the hub's Subscribe tab, where the hub will display a list of all the data providers it pulls from. You will need to enter the URL for the provider interface file for the data provider you wish to subscribe to.