A list with hubs will load automatically. And you can right-click on one and click on Connect. Which will immediately open a Hub window where you can see all users and communicate in the mainchat.
If no hublist loads the selected hublist might be down. Just select another hublist in the Configured Public Hub List box and click on Load Hublist.
Add a hub to favourites if you want to connect to it in future without the need to search for it in the hublist.