This question already has an answer here:
I have installed Ubuntu 12.10 on my Lenovo G550 laptop. It has a Broadcom 4312 Wireless LAN adapter which is not working.
04:00.0 Network controller : Broadcom Corporation BCM4312 802.11b/g LP-PHY [14e4:4315] (rev 01)
How do I fix it? How can I see what drivers are being used? I've downloaded what I think is the driver from the Broadcom site but have no idea how to get it installed.
Please keep in mind that I'm completely new at this Linux stuff.