Basically you need to follow the instructions supplied with the Livebox. If your PC is close to the telephone socket just set the LiveBox up there and connect to it using an RJ45 Ethernet cable supplied in the box - no need to make this a wireless connection. You can then connect to the Livebox Router Management pages through this cable to change the passwords (Necessary) and the SSID (Router Name) if you wish.
On the bottom of the Livebox will be an encryption key for the wireless. It will probably be WPA-PSK and consist of letters and numbers. Write this down and you will need to enter this in the laptop when it arrives.