Once you have purchased TableNinja you will receive an email with a purchase code within 24 hours (if you do not receive this email please be sure to check your spam folder). Run TableNinja and go to the Purchase/Update window under Help in the menu bar and copy this code into the text field labeled "Purchase Code" and click the "Try Purchase Code" button.
If your purchase code is valid TableNinja will be unlocked. If your purchase code does not work on the first try please double check that you've pasted the purchase code into the text field correctly. Depending on your email setup the purchase code may be two lines so make sure you've got it copied and pasted completely.