Just install it as other WordPress' plugin, click Add New in your WordPress plugins page.
After the uploading, remember to click activate plugin button.
Once the plugin active in WordPress, you will see a new Dashboard menu named Blacklist & Validation under Gravity Forms there.
The first screen will ask you to activate your license first. Just copy the license from your Purchase History to here and then click the button Activate License
Purchase Gravity Forms Blacklist and Custom Validation Pro