“Twice a day, sea water rises slowly and covers part of land, then falls back. High tide is when the water covers the most land. Low tide is when it covers the least amount of land.
The earth’s gravity keeps the water of the oceans stuck to the earth. And the moon’s weaker gravity pulls the water towards it as it passes over the oceans. When the moon passes over land, a bulge of water follows it until the moon goes too far over land and its gravity becomes too weak. That’s high tide and low tide for you!
Oh, and by the way, the piece of land between high tide and low tide is called the inter-tidal zone. That’s my area, see, and you are trespassing! So get out from my turf! It’s my busy time and I have to work, now. I’m not on a holiday, unlike you!”