The easiest way to get Lutro is by downloading and installing Ludo.
Ludo is like RetroArch an emulator frontend.
Think of it as a user interface that can run many retro games, including Lutro games.
You can download this example game that was created to help you get started with Lutro:
https://github.com/libretro/lutro-snake
main.lua
file.The game should launch.
You can also launch games using the CLI. Starting from the directory of Ludo.
./ludo.exe -L cores/lutro_libretro.dll path/to/lutro-snake/
./ludo -L cores/lutro_libretro.dylib path/to/lutro-snake/
./ludo -L cores/lutro_libretro.so path/to/lutro-snake/