Mr Optimistic,
Tides on Earth are caused by the minor influence of the Sun and (mostly the) Moon's gravity. When Moon is directly overhead, there's a little less net attraction of the water surface to the center of the Earth, and so there's a tidal bulge. Six hours later, there's a sideways pull from the Moon instead, and no such bulge. The gravitational field varies and shifts direction slightly at the Earth's rotation rate.
The bulge opposite the Moon needs you to shift into the rotating frame around the Earth-Moon system center of mass, and is less amenable to a one-line explanation.