Usually there's no need for Antivirus software on a Mac but should you have one please do pause it during the installation of our app.
Our app is notarized with Apple (meaning it comes from an official Apple Developer) so you can just double click on it and then drag it over to the Applications folder (same way as you install all other macOS apps):
When you start our app for the first time, it might ask for permission to access the Documents folder. Please do allow this so we can write your 23andMe email and password to your Keychain. In case you didn't allow, you can allow it later under Security and Privacy again:
On the first start, most likely it's downloading the newest update immediately, so give it some 30 seconds to do that. Then you can unpause your Antivirus app (if you have one installed).
Login with the email and password you used to register on our website. You will be prompted to also enter your 23andMe email and password (as those are now kept on your computer).