Ubuntu normally allow you to easily connect to wireless networks by just clicking the name of the network you'd like to use, but most wifi cards need a proprietary driver to work. So check on the top bar if you have a notification to install additional drivers or go to the "System Settings" > "Additional Drivers" to see if you need to install a proprietary driver for your wifi card.
If new drivers have to be downloaded, you'll need a wired connection to the internet before being able to use your wireless connection.
If no drivers is needed you will be able to see a wireless icon on you top bar of your desktop, so just click on it to see the available wifi networks around you, if you can't see your network, click on "More networks" and if your network is hidden, click on "Connect to Hidden Wireless Network..." and give the information it will ask you.
This answer is an adapted transcription of the following YouTube video: http://www.youtube.com/watch?v=NJvB97cmrWk