At the anode, hydrogen gas reacts with the OH- ions, producing water, and releasing electrons. The electrons go round the electrical circuit attached to the fuel cell, and reach the cathode. Here they react with the oxygen, and water, producing more OH- ions to replenish those used at the anode. The OH- ions move through the electrolyte, and the electrons move round the circuit. The complementary movement of ions and electrons is shown in the diagram below.
Water is produced at the anode twice as fast as it is used up at the cathode.
The cathode is the electricaly positive terminal, the one that the electrons flow towards. Some people find this confusing, since they are quite wrongly taught that the cathode is the negative terminal for everything. The cathode is also the correct name for the positive terminal of any primary cell.