Download the entire Cryptomatte GitHub repository using the green "Clone or download" button. Select "Download Zip" and then extract the contents.
Copy the fusion/Modules/Lua/cryptomatte_utilities.lua module into the standard Fusion Lua "package.path" location. The Lua modules can also be added to a folder that is listed in your LUA_PATH based environment variable.
Windows : C:\Program Files\Blackmagic Design\Fusion 9\lua\
Copy the fusion/Fuses/Matte/cryptomatte.fuse file into the Fusion user preferences based Fuses:/ PathMap directory, or the "Fuses" subfolder in the Fusion installation folder.
Windows : C:\Program Files\Blackmagic Design\Fusion 9\Fuses\
Copy the fusion/Config/cryptomatte_shortcut.fu file into the Fusion user preferences based Config:/ PathMap directory, or the "Config" subfolder in the Fusion installation folder.
Windows : C:\Program Files\Blackmagic Design\Fusion 9\Config\