Start off by connecting up with the supplied ethernet cable then in your browser address bar type in:
192.168.1.1 then hit enter
Login with the password admin
Go to Livebox - WiFi Settings choose a Livebox name if you want and then a security key (anything you want).
Select security mode WPA/WPA2 (TKIP/AES). Ensure 'Easy pairing' is ticked.
You will then need to change the security settings in all your wifi devices you wish to connect to the livebox.