Many students would still find it confusing to understand the phenomenon of high tide and low tide. What causes it and why?
Simple reason is to associate it to gravity of the Earth and the Moon, and the pull of force is called gravitational force. Gravitational force exists between two objects with mass. 
For smaller objects, this force is not very noticeable. However, for massive objects like the planets, this gravitational force creates a significant effect. Both the Earth and the moon exert a force towards each other. The gravitational force decreases with increasing distance, so the water nearest the moon is pulled more strongly towards the moon than the mass of the Earth itself. This force causes the water of the earth to swell on the area directly opposite the moon –which is called HIGH TIDE.
For smaller objects, this force is not very noticeable. However, for massive objects like the planets, this gravitational force creates a significant effect. Both the Earth and the moon exert a force towards each other. The gravitational force decreases with increasing distance, so the water nearest the moon is pulled more strongly towards the moon than the mass of the Earth itself. This force causes the water of the earth to swell on the area directly opposite the moon –which is called HIGH TIDE.