How many high and low tides occur each day

2 high, 2 low

Explanation:

The tides are created by a combined effect of the attractions of the moon and the sun.

Most places on Earth experience 2 high tides and 2 low tides in a period of 24 hours and 50 minutes, the duration of the moon day period (rotation of the  moon around the Earth).  

Due to the varying angles of the sun and the moon compared to the Earth, and the fact that the movement of the water around the globe is interfered by the continents, the tides are not always the same height.

Some places, due to specific geographic parameters, might experience only one high and one low tide, but most places do have 2 of each.