To disconnect from a network, click the Network Manager icon and choose Disconnect, underneath the name of the current connection.

To turn off a network connection (so that no connections can be made), right-click the Network Manager icon and uncheck Enable Networking.

You can turn off your wireless connection by right-clicking Network Manager and unchecking Enable Wireless. Some laptops have a switch or combination of keys that you can press to switch off the connection too. This is useful if you are using your laptop on an airplane or somewhere else that wireless devices are not allowed.