You have to implement all the components shown in blue. This library (@lumieducation/h5p-server) provides the parts in yellow and the grey parts are provided by Joubel's H5P client libraries (downloaded from the PHP implementation). The Express package (@lumieducation/h5p-express) deals with all AJAX calls by the H5P JavaScript client. You are free to use it, but can also implement the HTTP endpoints yourself.