Unlike windows you ought to configure your connection for each network. How did you configure the network before ?
You can download and use wifi-radar if you prefer simpler life. Sorry I don't know what tools debian provides. I use Gentoo and I use iwlist, iwconfig utilities to scan and configure wireless network.
Also, your local wireless network might not be free and some kind of WEP key might be involved. And I really can't guess what "unable to connect" would mean
. So please detail the procedure you are using to connect to the network and have a look at wifi-radar. Its quite similar to the windows wireless config manager.