The documentation is spit into parts by audience.
Are you building an ad plugin using videojs-contrib-ads?
Check out the integrator docs.
Are you contributing bug fixes or features to videojs-contrib-ads?
Check out the developer docs.
Are you adding advertising support to a video player on your site?
Please refer to the documentation for the ad plugin you are using. videojs-contrib-ads is a library for building ad plugins and is not a stand-alone ad plugin.