Click on Network under System Preferences
Click the + sign to create a new service
From the Interface pop down menu choose VPN
Change the Service Name to StrongVPN (L2TP) or whatever you like and then click Create
Click Authentication Settings
Put your password and shared secret in from your setup instructions email.
Hint: Your Password and Shared Secret can be found in the Customer Area (check here).
Put your server address and login from your setup instructions. Click Apply
Hint: Your Server Address and Account Name are also in the Customer Area (check here).
Click Advanced (after apply!) and check the box Send all traffic over VPN connection
That's it you are done, go to http://strongvpn.com and make sure you have the desired country IP of your VPN account.
Enter your email to try