At the beginning of the famously-terrible movie Waterworld, we see Kevin Costner peeing into a machine that converts his urine into drinkable water. It was futuristic in that movie, but it's actually a realistic concept.
The H2O is just such a pee filter. In order to use it, you simply urinate into it as you would any other toilet, then put the cover on it. You then squeeze it between your knees to get the filter working, and then drink from the spout at the bottom. Before all of this, you need to be OK with drinking your own pee, but I guess that step is just assumed.