This is a simple app template for Leaf - unlike the example within the Leaf repository, this keeps Leaf as an external submodule and is much more sensible for actually building applications. See the Leaf repository for more details.
Once you've cloned, you can customize the premake5.lua and LeafApp/premake5.lua files to your liking (eg. change the name from "LeafApp" to something else). Once you're happy, run scripts/Setup.bat to generate Visual Studio 2022 solution/project files. Your app is located in the LeafApp/ directory, which some basic example code to get you going in LeafApp/src/LeafApp.cpp. I recommend modifying that LeafApp project to create your own application, as everything should be setup and ready to go.