Click on "Get license online" and fill out the form. The license code will be sent to you. For free.
To add some info to Bob answer if you are using PSoC 4 and 5LP you can develop those with GCC compiler (comes with Creator and it's free :D), if you are using PSoC 3 i think this only use Keil compiler, as Bob says you can get the license for free.
You can say to Creator to don't display this Window when you start Creator software:
With Creator opened go to Tools menu, then choose Options and you have to check a box, then Apply button and OK, i attach a image of the Options window
Hope it helps