Connect to a VPN
A VPN (or Virtual Private Network) is a way of connecting to a local network over the internet. For example, say you want to connect to the local network at your workplace while you're on a business trip. You would find an internet connection somewhere (like at a hotel) and then connect to your workplace's VPN. It would be as if you were directly connected to the network at work, but the actual network connection would be through the hotel's internet connection. VPN connections are usually encrypted to prevent people from accessing the local network you're connecting to without logging in.
There are a number of different types of VPN. You may have to install some extra software depending on what type of VPN you're connecting to. Find out the connection details from whoever is in charge of the VPN and see which VPN client you need to use. Then, open Ubuntu Software Center and search for the network-manager package which works with your VPN (if there is one) and install it. You will need to click the Show technical items link at the bottom of Ubuntu Software Center.
If there isn't a NetworkManager package for your type of VPN, you will probably have to download and install some client software from the company that provides the VPN software. You'll probably have to follow some different instructions to get that working.
Once that's done, you can set up the VPN connection:
Click the network menu on the menu bar and, under VPN Connections, select Configure VPN.
Click Add and choose which kind of VPN connection you have.
Click Create and follow the instructions on the screen, entering details like your username and password as you go.
When you've finished setting-up the VPN, click the network menu on the menu bar, go to VPN Connections and click on the connection you just created. It will try to establish a VPN connection - the network icon will change as it tries to connect.
Hopefully, you will successfully connect to the VPN. If not, you may need to double-check the VPN settings you entered. You can do this by clicking the network menu, selecting Edit Connections and going to the VPN tab.
To disconnect from the VPN, click the network menu and select Disconnect under the name of your VPN connection.