Atheros and Broadcom are the two most popular manufacturers of Wifi cards. However, support for using Wifi with them is not present out of the box in Ubuntu Linux.
I had covered installing Wifi on Ubuntu for Atheros Wifi cards earlier in this post.
To install Wifi for Broadcom on Ubuntu, follow the steps below.
If you have a working Internet connection of any form, other than the non-functional Wifi, you can select to install the package named b43-fwcutter, which will do the Wifi driver installation along with the installation of the package itself. Your Wifi should work fine after a restart.
Now, open a terminal and install the driver with the commands,
sudo b43-fwcutter -w /lib/firmware wl_apsta-18.104.22.168.o
tar xfvj broadcom-wl-22.214.171.124.tar.bz2
sudo b43-fwcutter --unsupported -w /lib/firmware broadcom-wl-126.96.36.199/kmod/wl_apsta_mimo.o
Finally, restart your computer to verify if the Wifi is installed.