Why there are tides
Twice a day, on almost every coast, the sea level rises and falls. The Moon is mainly responsible: its pull draws the ocean water, raising a bulge on the side facing it and another on the opposite side.
When the Sun and the Moon line up, their pulls add together and the tides are larger; when they form a right angle, the tides are smaller. The shape of the coast and the depth of the sea change the timing and height in each place.