Your download of Columnal version 0.6.4 for MacX86 will begin automatically in 5 seconds.
The download is a .dmg file. Open it from your browser's downloads, and a window should pop up. Drag the Columnal icon on the left onto the Applications folder on the right. If you're upgrading, agree to overwrite the old version (make sure Columnal is closed first). Then you should be able to launch Columnal from your Applications folder like any other application.
Note for users of MacOS 10.15 (Catalina) or later: Columnal should work with the new app notarization security checks. If you have any troubles, email earlyaccess@columnal.xyz.
Columnal is currently in early access, which means the design is still being worked on, and the last few kinks are being ironed out. If you have any problems or suggestions, drop an email to earlyaccess@columnal.xyz where we will be happy to hear from you.