how do I add a new device?

Hi pritch
 
Welcome to the Community Forums.
 
As long as your subscription is for more than one device (I am assuming that you already have WSA installed on another, older PC?) then all you need to do is to:
 

• Make sure you have a copy of your Keycode
• KEEP the computer online for the install to make sure it works correctly
• Download a Copy of the PC version Here (Best Buy Subscription PC users click HERE)
• Install with the new installer, entering your Keycode when so requested by the installer
• Let it finish it's install scan
• Reboot once again

Now, if you only have a 1 device subscription you will need to deactivate the old PCs protection first by going into you online console (here). Instruction on what to do to undertake the deactivation can be found in this KB Article.
 
Hope that helps? If you have any follow up question please post back here and we will see what we can do to assist further.
 
Regards, Baldrick