Start by opening https://tunnelblick.net/ with Safari or the browser of your choice. Go to "Downloads" and click on the "Stable" version of Tunnelblick.
After the download has finished, click "Downloads" and then click on "Open in Finder".
You will see the downloaded disk image in Finder. Double-click the file.
The Tunnelblick installation program must be started by another double-click on the Tunnelblick icon.
Because Tunnelblick has been downloaded from the internet, there is a security popup. Choose "Open" - you can optionally choose to never be warned of this again.
In order to allow installing an application, you have to type your password next.
When the Tunnelblick installation is ready, Tunnelblick asks you for configuration files. Choose "Quit" here now.
Now is a very good time to delete the Tunnelblick disk image file. It can confuse Finder, so do it.
The Tunnelblick disk image is removed. Just to be sure, see if your status bar has an icon indicating a running Tunnelblick instance. If there is an icon, "Quit Tunnelblick" now.
Now, get back to your browser and enter https://hometunnel.net. If neccessary, sign in. Choose "Settings" and click on the "Admin" button in the detail view.
That should take you to your local HomeTunnel box interface - if you do not see the login screen, you may have tried to setup your Mac while not being connected to your home network. Sign in (the password is probably still "hometunnel" - if so, please change it!).
You should be on the "Credentials" page now. You can click on both credential downloads now. Afterwards, click on your Mac OS "Downloads" and choose "Open in Finder".
Now the credential files are visible in the Finder window. Double-click one of the files in order to import them in Tunnelblick. Always assure that Tunnelblick is stopped for this to work (i.e. there is no visibile Tunnelblick icon in the status bar).
If all went well, Finder should now open Tunneblick with the credential file. The security prompt shown above only appears if you did not check the "Don't warn me again..." box earlier. Press "Open" in this case.
You must now choose if the credential profile shall be installed for all users of this Mac or just for you. Usually, you would choose "All Users".
In order to install a VPN configuration, Tunnelblick always asks for your password.
On the Mac OS status bar, there is a Tunnelblick icon now with a menu that should look like this. You can click on "VPN Details" to see your VPN log and settings.
When you click on it, you see this window. You can add and remove profiles, connect and disconnect and choose advanced settings here. Press "Connect" now.
After a short time, there should be a popup indication that your VPN connection is up. Congratulations! Now "Disconnect" the VPN tunnel.
You can import the second credential profile now from the Finder window. Sometimes, this does not seem to work, i.e. that nothing happens on double-click. In such a case, close Tunnelblick by choosing "Quit Tunnelblick" from the icon menu and try again. Beware: Closing the VPN detail window does NEITHER quit Tunnelblick NOR stop the VPN!