This article is excerpted from the newly published book The Official Ubuntu Book and is found at Linux.com
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Simply click on the Network-Manager icon to see all available wireless networks, and click on the network to connect to it. If wireless authentication is needed, be it WEP, WPA, or 802.1x, a network-manager dialog will pop up asking for your authentication details.
If network manager does not solve the problem, the first step should be to see which driver your wireless card needs. Do a search for your card on Google and in the Ubuntu Forums to find out which driver you need. Many of the drivers are already included in Ubuntu, but some newer drivers may not be present.