1. Download myTaxExpress or T2Express Mac version software (a .zip file)
2. Right click the downloaded .zip file with mouse, choose open from popup menu. It will unzip the program into your computer. It will create an App, like "mytaxexpress2012_netfile" for tax year 2012.
3. Since Mac OS Sierra update, it's required that you copy the unzipped app into Application folder. For detail, you can also read this FAQ item.
4. Double click the "mytaxexpress 20xx" icon from Application folder to run myTaxExpress.