Grab the installer for your platform from the download page. Black Diamond Distortion ships as VST3 on all platforms, plus AU on macOS. Each installer also includes the factory presets, transfer functions, and impulse responses.
macOS
Run the .pkg and follow the prompts - you’ll be asked for an admin password, and you
can choose whether to install the AU, the VST3, or both. The installer is signed and
notarized, so Gatekeeper won’t complain. Plug-ins land in the system folders
(/Library/Audio/Plug-Ins).
Windows
Run the .exe installer. The VST3 installs to
C:\Program Files\Common Files\VST3 by default (you can pick a different folder in
the wizard), and a previous version is removed automatically first.
Linux
Extract the .tar.gz, then from inside the folder run sudo ./install.sh for a
system-wide install - or ./install.sh --user to install into ~/.vst3 without root.
One caveat: the factory impulse responses are only picked up from the system location,
so prefer the system install if you want them. ./install.sh --uninstall removes
everything again.
After installing
Restart your DAW (or rescan plug-ins) and it will pick the plugin up automatically.