How the Moon creates tides
The Moon's gravity pulls on Earth's oceans, creating a bulge of water on the side of Earth facing the Moon. At the same time, another bulge forms on the opposite side of Earth. As Earth rotates, different parts of the ocean move through these bulges, causing the water level to rise and fall. This is why most places experience two high tides and two low tides each day.
The Sun's effect on tides
The Sun also pulls on Earth's oceans with its gravity, though its effect is weaker than the Moon's because the Sun is much farther away. When the Sun and Moon line up on the same side of Earth, their gravitational pulls work together to create extra-high tides called spring tides. When the Sun and Moon pull at right angles to each other, their effects partly cancel out, creating smaller tides called neap tides.
Why tides matter
Tides affect ocean currents, coastal ecosystems, and human activities like shipping and fishing. Some coastal areas experience dramatic tidal changes of 30 feet or more, while others see only a few feet of difference. Understanding tides helps scientists predict ocean behavior and helps people who live or work near the coast plan their activities.
The role of gravity
Gravity is an invisible force that pulls objects toward each other. The Moon's gravity is strong enough to pull on the entire ocean, even though the Moon is about 240,000 miles away from Earth. This gravitational attraction does not require the Moon to be touching Earth or even close to it—it works across the vast distance of space. 
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