Wanting to hook up batteries to 3 servos

I want to hook up 3 servos to some batteries. Since it show it operate at 4.8v and 6v, that mean I need 6v to get the most out of one. Does that also mean I just need 6v for altogether to make them all move. They will all be moving at the same time. I figure I would need more V then that but maybe it would have to do with mah. Could someone explain how it able to all three use the same power source. Also does having more mah mean the battery last longer or make it stronger??? thanks in advance.