A common question for people discovering this project is: How do I easily add desktop support to my existing Flutter application?
The answer is that at this point, you don't. The project is still in early stages, and a lot of things are still in flux; if you don't already have experience doing desktop development on the platform(s) you want to add, this project is probably not ready for you to use it yet. The focus is currently on improving core functionality, not on ease of use. Neither the API surface nor the project structure are stable, and no attempt will be made to provide supported migration paths as things change.
However, if you want to try out an existing Flutter application running on the desktop even with those caveats, and don't have experience with desktop development, here are two approaches that might work for you.
With either approach, be sure to follow the main README and library README instructions on setting up prerequisites and adjusting your Flutter application.
Since example/ is already configured to run on all the platforms this project
supports, you can swap in your project's Dart code, pubspec.yaml, resources,
etc., then follow the normal directions for building the
example application on your platform.
This will be the easiest approach to keep working as the project changes, but requires that you essentially wrap your whole application in a flutter-desktop-embedding checkout.
Starting from the example projects means you don't have to create projects from scratch, and since they are self-contained they can be added to an existing project without needing to move it. However, because the projects build the flutter-desktop-embedding libraries from source, they contain relative paths to the flutter-desktop-embedding projects and tools they depend on. You will need to update those paths in order for the projects to work. On Linux, the variables you will need to change are documented in the Makefile. On macOS and Windows, you will need some familiarity with Xcode and Visual Studio respectively to make the changes.
With this approach, you should expect breakage when you update the flutter-desktop-embedding reposity; when that happens you will need to look at what has changed in the example projects and update your copies accordingly, or start over with fresh copies and adjust the paths again.