Why do tides rise and fall?
The short answer
The Moon's gravity and the motion of the Earth–Moon system create broad bulges of ocean water, causing sea levels to rise and fall.
How it works
Water on the side facing the Moon is pulled more strongly, and another bulge forms on the opposite side because of the shared motion of Earth and Moon. As Earth rotates, coastlines pass through these bulges.
A familiar example
The shape of a bay and the depth of the seafloor can make local tide heights and timings different.