Follow the documentation to install navground. This plugin does only depends on the navground_core and navground_sim C++ shared libraries.
You can install navground from source or install pre-build binaries.
Once installed, will need to source the environment to find navground
$ .<navground_install>/setup.zsh
$ .<navground_install>install/setup.bash
$ <navground_install>install\setup.bat
where <navground_install> is the directory where you installed navground (e.g., /opt/navground/ on Linux and macOS and C:\ProgramFiles\navground in Windows).
When installing from source, you are free to build navground in the same colcon workspace or in a separate location, provided you source the environment.