1. Clone repo
2. Open project in Unity
3. Run Assets -> External Package Manager -> Import All
4. Load the basic example scene showing level loading (cube prefabs) and platform UI: \Assets\External\TimeWalk\Example\Scenes\Master.unity
5. If there are errors it is likely the package import failed. Try downloading the packages referenced in /Assets/packages.json and manually importing them.

See the wiki for more info.