Beer draft system

Klarstein beer tap. Bought about five years ago as a gift -- tried to use it once, couldn't figure it out! Here is the link to the model https://www.klarstein.cz/Klarstein-Skal-vycepni-zarizeni-chlazeni-piva-5l-soudek-CO2-uslechtila-ocel-Stribrna.html