The level of the sea rises and falls about two times each day. We call these changes tides.
The gravitational pull of the Moon creates tides on Earth . The Moon's gravity pulls the Earth's oceans towards the Moon. This causes a high tide on the side of the Earth nearest the Moon. However, on the opposite side of the Earth, furthest from the Moon we also see a high tide!
The Sun's gravitational pull also has an effect on Earth's tides. When the gravity of the Sun and Moon are pulling in the same direction, the tides are especially high. We call these 'Spring tides'. Spring tides happen at full Moon and at new Moon.