As TheChair indicates, a Freeview TV set can serve two purposes. Firstly it can display the picture from its own built-in Freeview tuner (when there's a terrestrial aerial connected, of course) but it can also act simply as a monitor, to display the picture from any suitable external source (such as a DVD player or Freesat box).
You'll simply need to connect the Freesat box to the TV with an HDMI (or Scart) cable and then set the appropriate source on the TV set. That's usually achieved by pressing the 'Source' button on the TV's remote control (which is often labelled by a rounded rectangle with an arrow pointing into it), navigating to 'HDMI 1' (or whatever is appropriate, by pressing the 'Up' and 'Down' buttons on the remote control) and then pressing 'OK'. Once that's done you'll be able to see the output from your Freesat box on the screen.
Unless you've got a remote control which works with both devices, you'll need to use the one for the Freesat box to change channels but the one for the TV to adjust the volume.