If the box has wifi, Settings/Connections/Wifi
Select your signal, put in the password (call them if they put in a password without telling you what it is, or didn't tape it to the bottom of the box) and it should connect.
If there's a WPS on the box (Wifi Protected Setup - it may be a button that has "refresh" arrows in a circle), just press the button and if you have wifi enabled on your phone, it will connect by itself.