Once you've purchased the plugin, you'll get an email with a download link to the zip file.
You can also download the plugin zip file directly from flying-press.com/account -> View Details and Downloads
After downloading, upload the zip file by going to Plugins -> Add New -> Upload Plugin
FlyingPress will start optimizing pages only if the license is activated.
You can find the license key in the email you've received after purchase. You can also get it from flying-press.com/account -> View Details and Downloads
To activate the license, go to FlyingPress -> License. Enter the license key and click 'Activate License'