You can purchase a license via the iTunes App Store (by clicking the grey "App Store" image to the right) or directly from your iPhone or iPod Touch. Just search for "iAffirm" within the App Store on your awesome little device.
Your application, after purchasing, will immediately begin downloading to your computer, iPhone, or iPod Touch. There is no license file to handle and your application is fully unlocked and ready for your use as soon as it finishes downloading. If you download to your computer, you will have to sync your iPhone or iPod Touch to copy the application to your device.
All minor feature updates (1.x) and maintenance releases (1.x.y) are free for existing customers. We are not yet sure how Apple handles upgrades, but it's our intent, if allowed, to offer a discount when we reach such a point. At this time, we do not plan a 2.0 release, and all upgrades should be free for quite some time.