you need to go to settings tab on your chromebook and click on internet tab. now you will able to see an option for add network click on that and select private network.
finally you will get an option for server address. you need to fill there your server address and click ok save settings or ok.
now your password will be setup.
You need to go to settings on your chromebook and select internet connection.
Now you need to click on add connection, and click on private network.
Finally there will be a box open on your computer. you need to go ahead and fill the server address there and follow the instructions .
Google has a how-to guide on how to set up a VPN on a Chromebook:
1. If you haven't already, sign in to your Chromebook.
2. Click the status area at the bottom of your screen, where your account picture is located.
3. Select Settings.
4. In the "Internet connection" section, click Add connection.
5. Select Add private network.
6. In the box that appears, fill in the information below. If you're using your Chromebook with an organization, you may need to get this information from your network administrator.
*Server hostname: Name of the server that you need to connect to in order to access your VPN. This can either be the IP address or the full server hostname.
*Service name: This can be anything you want to name this connection, for example, "Work VPN."
*Provider type: If you use a passphrase or key besides your personal password to connect to your VPN, select L2TP/IPsec + Pre-shared key. If you use certificates that your network administrator gives you, select L2TP/IPsec + User certificate.
*Pre-shared key: The Pre-shared key is not your personal password, but a passphrase or key used to connect to the VPN.
*Server CA certificate: Select your installed server VPN certificate from the list.
*User certificate: Select your installed user VPN certificate from the list. If you don't have any certificates installed, you'll see an error message. To install a certificate, see instructions below.
*Username credentials for connecting to VPN.
*Password credentials for connecting to VPN.
7. Click Connect.