Does it detect your network card? Look up at the notification area (the Linux equivalent of Windows' System Tray) and see if you have a networking icon (two computers). If you do, right click it and it should show wireless networks available if your card is set up correctly. If they show, just pick your connection and enter your WEP/WPA key. If they don't show, or you don't have a wireless device listed at all, try using the Restricted Drivers Manager (might be like Hardware Drivers in the new Ubuntu, it's in System>Administration) to install firmware or drivers. If you're using a Broadcom card (many cards are Broadcom, they're pretty common), then you'll need a proprietary firmware which the manager will install for you. If you're using Intel wireless, it should have automatically installed when you installed Ubuntu.