On eNotes, we cannot actually write a story for you. We can help you understand how to do your work but we cannot actually do your work for you. I will define the terms you are asking about and give you a suggestion about how to write a story.
Bay: A sheltered body of water that is blocked off to some degree by land from the larger body of water of which it is a part.
Channel: There are three definitions for this. It can be A) a wide body of water between two pieces of land that are near to one another; B) the deepest part of a river or other waterway; or C) a narrow body of water that connects two other, larger bodies of water such as two lakes.
- Island: A piece of land completely surrounded by water.
Isthmus: A narrow strip of land that has bodies of water on either side and connects two other, larger bodies of land.
Peninsula: A piece of land that is surrounded by water except on one side, where it is connected to a mainland.
Plateau: A large, flat, landform that is higher than the surrounding land. It must rise sharply from the surrounding area on one or more sides.
If I were going to write this story, I would have someone who was up on a plateau, keeping watch over the ocean. Maybe they are waiting for a ship to come in bringing loved ones or maybe they are worried about pirates or other attackers. I would describe each of the terms as I told the story. So it might begin something like:
The two sentries stood high on the plateau, on the lookout for enemy vessels. Around them, the plateau dropped away steeply to the plains below. The plateau stood on a peninsula. To the east, there was a large bay, sheltered from the ocean on one side by the peninsula.
You could go on, describing the landscape over which the sentries are looking. That way, you will have the definitions of all of the terms you need incorporated into the story.