This theme was created for the Substratum theming solution.
This means that it will not provide any functionality on its own, but work in an add-on style with the above mentioned app, developed by a different team of developers.
It seems like you have not installed the Substratum app on your device.
If you still want to use this theme, please try to get the Substratum app to work on your device first.
Unfortunately, Substratum will not work on all devices. Usually it requires a rooted device or a custom ROM with inbuilt Substratum support.
Please also keep in mind that for an optimal experience, a custom ROM with the required Substratum support is recommended. This theme *might* also work on stock ROMs if they are close enough to the original Android code and Substratum works on them, but this is not officially supported.