An unsecured WiFi network is unsecured -- it won't work to turn WEP or WPA encryption on at your computer if the WiFi router isn't configured to use it as well. And, then you have to know the encryption key to type in to make the connection. So, best practice is to only connect to secured networks to which you have access to the key.
If you do choose to attach to unsecured "public" networks, understand that you are pretty much wearing red on Rush Street. Don't enter any passwords, credit card numbers, account numbers, or anything of the sort. Also, within the Windows
Wireless Network Manager, there is an option for whether or not you connect to ad-hoc (peer-to-peer) networks. It is allowed by default, but you want to turn it off to prevent you from connecting directly to some bad guy's computer.
It is also a good idea to create a separate user on your computer that you use when you are going to connect to public sites. Give it only "guest" privileges to prevent a potential hacker from installing anything on your computer such as "phone home" malware or keystroke loggers.
To check your mail, change your password ahead of time for when you will be connecting to a public WiFi, and then change it again after you are done. Frequent password changes stymie even the best hackers.
The subject of WiFi security can be discussed forever, but the bottom line is that even with the best diligence, it really isn't all that secure, so treat it that way.
On other thing -- only connect to public sites that you KNOW are legit. Don't connect to an unsecured site just because it is there and has a good signal. Not only is it dangerous, it is also illegal unless permission is expressly granted. Legal precedent has consistently ruled against the user, often with startling fines, and sometimes even jail time.