Drag and drop the WhatSize.app into your Applications or Desktop.
Than start up the application and enter the license info like so.
Step 1, Click on menu item "License ..."
Step 2, Click on the "Add License ..." button
Step 3, Look up in your confirmation email for the "Registration Information" block.
Look for a block that will resemble the following
Registration Information:
Serial Number Name:
John Doe
Serial Number:
WHATSIZE-XXXX-XXXX-XXXX-XXXX-XXXX
Copy paste the values from the email to the matching User Interface Text Fields in the screen below.
For example copy John Doe into the TextField named Serial Number Name: (first row)
and WHATSIZE-XXXX-XXXX-XXXX-XXXX-XXXX into the TextField named Serial Number: (second row)