You can access the wireless network from anywhere in College Library. If your laptop's wireless card is turned on and configured correctly, you should be able to simply open a browser and try to go to a web page. The wireless network will redirect you to the wireless login page. (You will need a valid UW-Madison NetID to authenticate.)
Once you authenticate on that page, your computer will have access to the wireless network.
For more information about the campus wireless network, go to: http://www.doit.wisc.edu/network/wireless