Explain how the position of the moon relates to the occurrence of high tides and low tides?

The closer the moon is to earth, the greater the moon’s gravity pulls on earth causing high tides. Low tides occur between two high tides.

There are 2 high tides and 2 low tides on most days. 

A high tide occurs near the point directly "under" the moon AND at the point on the opposite side of the earth.. 

Low tide occurs near the time when the moon is near the horizon. 

A more detailed

The high and low tide are caused by the gravitational forces between the earth and the moon. However, the source of the real effect takes some explaining to grasp. The incorrect way of thinking is that the moon attracts all the water to itself, therefore causing a high tide on the side of earth close to the moon, and a low tide on the side far from the moon. However, if this was the case, there would be a high tide once per day. But there are TWO high tides a day. The reason is, the part of the earth both AWAY from the moon, and CLOSE to the moon BOTH get high tides... 

This is because the earth and the moon rotate around each other, each pulling the other towards itself. The moon attracts every piece of matter on earth. Since gravity is inversely proportional to the square of the distance, this force is greater on the side of the earth closer to the moon, and lesser on the side of the earth further from the moon. Since the earth is quite a rigid object, this difference in forces fails to deform the earth (much). However, it succeeds quite well in deforming the oceans -- which are not as rigid. Since the waters on the moon side are attracted more strongly than average, they tend to bulge TOWARDS the moon, hence causing a high tide. The waters on the opposite side of the moon, since they are attracted less strongly than average, tend to 'lag behind' the rigid earth, and bulge AWAY from the moon, which in this case, is also AWAY from the earth, again, causing a high tide. Low tide occurs at about right angles to the moon, where the force on the waters match the average pull of the moon on the earth closely.