This Flutter project provides the supporting code for the tutorial First steps with Flutter: Exploring widgets. Check it out for more details.
Flutter has a reputation of having a steep learning curve. If you take little steps, though, it isn't that difficult. By playing around with simple examples like the ones here, you will be up and running in no time.
If you don't have the Flutter development environment set up, you can find the directions to do that on the Flutter site. After that you can clone this repository and run it in Android Studio or Visual Studio Code.
Alternatively, you can just just start a new Flutter project and then just paste in the main.dart file.