The Earth's oceans experience two high tides per day. The location that is nearest to the Moon is the location furtherst away 12 hours later.

They occur on opposite sides of the Earth at the same time because of the difference in the Moon's gravitational field at the Earth's surface and at its center. The water gets pulled more than the Earth when it is closer to the Moon and less than the Earth when it is further away than the Earth's centre from the Moon.


The tidal effects are greatly exaggerated in the diagram - otherwise you would not be able to see the 'bulge'.