You can only do this to view passwords of connections that you are or have been connected with, you cannot use it to retrieve passwords of connections you have never been logged in with! That makes it a tool to remember what password you set here or there.
To view a password, left-click the connections icon in Windows' taskbar and go to the Network and Sharing Center:
On the left pane, click Manage wireless networks. You will see a list of items here, these are all the wireless networks you have been in so far with your machine. Right-click any of then and select Properties. In the appearing window, switch to the Security tab. You can see the encryption type as well as your password here. Just click on Show characters so the clear text will be visible: