1) Go to "Settings > General > VPN"
2) Choose "Add Configuration"
3) Fill your VPN login details as on figure (do not remeber to fill Secret field):
4) After you create a VPN configuration, the option to turn VPN on or off appears in Settings. When you connect using VPN, the VPN icon appears in the status bar.
If you use multiple VPN configurations, you can switch configurations using Settings > General > VPN.