As @TechMedX said, I'd suggest using Hubitat Package Manager. The packageManifest.json file is meant to be used with that app, it is not a Hubitat app in and of itself.
If you are installing manually instead of using HPM, you need to install the groovy file that is under src/apps in Apps Code, and add whichever devices you need from src/drivers to Drivers Code on your Hubitat.
Seriously though, save yourself some time and just use [BETA] Hubitat Package Manager
