You need a good broadband speed and have to connect the box to the router by cable.
You can watch Catch Up TV from iPlayer, 4OD etc via the internet on your tv. You can already watch these on your pc or laptop.
You can pause live tv, providing one of two tuners isn't been used for recording - it simply records the tv programme so it plays from where you paused.
You can watch a selection of free archive programmes 'on demand' and also pay to watch recent films. Again these come over the internet, so if your broadband isn't up to scratch you won't get a good service.
You still only get Freeview live channels.