Android platform included support for PPTP, L2TP and IPSec-based VPN connections.
This article will give an overview of where to find the settings  governing VPN connections, what connection settings are required, and  how to install and select certificates.
VPN settings are located in the Settings menu under Settings --> Wireless Controls --> VPN Settings:

The following types of VPN connection are supported:
- Point to Point Tunnelling Protocol (PPTP) 
- Layer 2 Tunnelling Protocol (L2TP) 
- Layer 2 Tunnelling Protocol with IPSec Pre-Shared Key 
- Certificate based IPSec VPN with optional L2TP shared secret 
 
PPTP
 
Adding a PPTP-based VPN connection requires only that an  identifying name be entered for the connection, and the name or IP  address of the VPN server:

DNS Search domains can be entered, to identify 'domain.com' as  sitting 'behind' the VPN and to use the remote DNS servers on that  network when searching for entries within the specified domain.
Once saved, the VPN connection will be listed:

Tapping and holding on the entry for the connection will display a  context menu allowing you to initiate the connection, edit it or remove  it:

Initiating the connection will prompt you to enter your username and password:
 
L2TP
 
Adding an L2TP-based connection is almost identical, except that  you can select to use a shared secret and configure the details of that  secret:
 
L2TP / IPSec PSK
 
The IPSec Pre-Shared Key L2TP-based VPN requires the same settings, but also allows for an IPSec key to be configured:
 
L2TP / IPSec CRT
 
Certificate-based VPN connections require that server and user  certificates be installed on the device. These need to be exported from  the VPN server in .DER format and copied onto the device. These can be  loaded from the SD memory card, or can be downloaded via the browser.
ADDENDUM - whilst I found on the unit used to create this article  originally that DER certificate files were required, if you find that  opening your certificate in the web browser simply downloads the text  content of the file, try using CRT format files instead.
When installing the certificate, you will be prompted to enter a name to identify it:

If you are prompted to enter a password before you can import the certificate:

this implies that the 'Secure Storage' feature has been enabled on  the device. This is configured within Settings --> Security:

Once the certificate has been installed, when creating the VPN  connection, the certificate will appear in the list of available  certificates:
 
   
with the name you entered to identify it.
Your VPN connection has now been configured. For details on troubleshooting mobile VPN connections, read this article: 
http://blog.brightpointuk.co.uk/troubleshooting-mobile-vpn-connections
For details on how to tunnel VNC via SSH on Android, read this article - 
http://blog.brightpointuk.co.uk/connect-ssh-vpn-vnc-android-device