According to Science and the Sea, lunar tides are the most common tides and are caused by the Moon's gravity. Although the Sun's gravity is stronger, it is farther from the Earth than the Moon, which is why lunar tides are more than two times stronger than solar tides.
Science and the Sea, a production of The University of Texas Marine Science Institute, explains that lunar tides are formed when the gravity of the Moon pulls more strongly on the side of the Earth facing it and creates bulges in a body of water. When the Earth rotates on its axis, the bulges also move and cause high tides when they hit land. Low tides are created halfway between the high tides when the water is at its lowest level.