The easiest way to install Camtasia on you Mac after making a purchase would be to access the email with the download link and software key in it on your Mac. Simply install from there. If you purchased the software directly through our store while logged into your TechSmith account, you can access your products at https://myaccount.techsmith.com/ (if you were not logged into your account, you can add the purchases there too). You would then access the Account page on your Mac and download the appropriate installer.
P.S. Kindly reminder that you must be the primary user of the secondary machine and that you cannot be running Camtasia at the same time (meaning you cannot be recording, editing, or producing on one machine while recording, editing, or producing on the other).