Hopefully you have a cable connected.
The bcmwl driver is available in the repositories.
Open a terminal and run these commands
Unplug the cable and click on the 'Network' icon, any available networks? If yes choose yours and enter the password for the router.
sudo apt-get install bcmwl-kernel-source
sudo modprobe wl
If none show leave the cable unplugged and reboot the system, it should be working now.
If not working after the reboot post the terminal output of
lshw -C network