As default, Ubuntu GNU / Linux doesn't support broadcomm WLAN (WiFi) adapter. And so, if you have laptop / netbook with broadcomm adapter, you won't be able to connect to the internet throughout WiFi / hotspot connection.
But luckily, Ubuntu makes it very easy to install broadcomm WLAN adapter. There are two easy options to install it :
1. By APT
Plug your laptop in to a wired (cable) internet connection and install the driver by following command :
sudo apt-get install bcmwl-kernel-source
2. By Ubuntu Live CD / USB
In your Ubuntu Live CD / Live USB, find a folder named pool. Find these files :
Copy those files into your home, open terminal, and install them by following command :
sudo dpkg -i *.deb
And now, you will have your broadcomm WLAN / WiFi works.