Because the ocean is a liquid, it is able to flow, the moon pulls the ocean, and the tides follow the moon. Not so, though, distance also plays a part in gravity. The distance from the earth to the sun is 93,000,000 miles, the distance from the earth to the moon is only 239,000 miles. The moon is much closer to us, and so the Moon Control's the Tides. There are many parts the moon plays in controlling the tides, there are also parts played by other important forces, these are called the tide producing forces.
High tide is basiclly when the moon is most over head.
If we were to have a world with no land interfereing with the flow of tides, directly under the moon, the water would bulge towards it's pull. There is one high tide. At the excat oopposite of the earth there is another high tide there. The reason for this is what we call centrifugal force. Centrifugal force tends to propel things outward.