When you subscribe to PSEngine, you will receive an email with your license key as well as a set of instructions with links to download the software.

You must download, and install the software on your PC/Laptop/Macbook. Once installed, open the software and you will be presented with a License window.

Copy and paste your license key in the field as shown below (with no spaces at the end). 

Then click Save and then click Activate.

Your software is now licensed and all functions associated with your subscription will be available. You can see the status and expiration date of the license in this window also. It can be opened from within the software from Config | License