Creating a template-based project
The instructions to create a template project can be found in the osu-framework repo, but they are fairly simple.
First install the NuGet package containing the template pack. If it is already installed, this command will update it to the latest version:
dotnet new -i ppy.osu.Framework.Templates
Then, simply create a new project using the template:
dotnet new osu-framework-game -n MyNewGame
You can replace osu-framework-game with osu-framework-flappy-game. MyNewGame can be replaced by the name of your game.
TemplateGame (Empty Template)
The osu-framework-game template contains a very basic game, with just a spinning sprite box and some text on a pink background. It uses a ScreenStack that sits in a DrawSizePreservingFillContainer to ensure content scales with all screen sizes. The test project contains a standard test browser with some basic visual tests.

FlappyDon (Flappy Bird clone)
The osu-framework-flappy-game template implements a Flappy Bird clone in osu!framework. In addition to the functionality in osu-framework-game, it shows how to handle input, play sound samples and handle game state in a basic way. It doesn't serve as a better base for a game than the empty template, but it can be a good, albeit basic, resource to learn about the framework.

There are many concepts not explained by the FlappyDon template such as UI tests, custom fonts and screen stacks. therefore, it is best to read through the osu!framework source code, through the source code of games made with osu!framework (such as osu! itself) or to read the rest of this unofficial documentation.
Note about assets: the FlappyDon game contains assets from various sources. Excluding the assets taken from osu-resources, they were all originally licensed under permissive licenses and don't require anything more than the MIT license requires. The osu-resources resources were originally licensed under CC-BY-NC 4.0, but are now licensed under the MIT license since they are in the osu-framework repository and don't explicitly have another license. This means you should be free to use all resources in this template.
Last verified against v2021.714.0