Like any other cragl product, smartCommand can be installed with cragl connect directly inside Nuke.
Open connect and drag smartCommand to the right to reveal more information. Just click on buy (1) and you will be located to the web page where you can purchase smartCommand.
After purchasing you will receive a mail including an install code. Now simply click on install now (2), enter your received install code (3) and smartCommand will be installed automatically on your machine.
Like any other cragl product, you can download a trial version of smartCommand that is equal to the full version of smartCommand. Right inside connect click the trial button to download your trial version.