The continental shelf is the border of a continent that is below the water. It gradually slopes down and away from the shore. The continental shelf is the shallowest part of the ocean floor. Marine life flourishes on or near the shelf. Most people enjoy "swimming in the ocean" at the beach. They're actually just swimming in a very shallow part of the continental shelf.
Continental rise and slope
The continental rise is the transition area at the end of the continent where the ocean floor begins and the continent ends. The continental slope is the steep incline towards the ocean floor. When the slope ends, the rise begins. The continental rise is sometimes considered to be part of the abyssal plain.
Oceanic trenches are big, deep, slices in the ocean floor. They can vary from thousands of meters deep to just a few hundred feet. A good example of an oceanic trench is the Mariana Trench. It is 11,035 meters below sea level. The Mariana Trench is the deepest oceanic trench man has discovered. It is the closest point of Earth to the mantle. Trenches are formed when one plate dives down below another. Where they meet is the bottom of the oceanic trench.
The abyssal plain is the actual ocean floor. It is mostly composed from eroding earth, or run-off sediment, from the continents and the surface of the water. The abyssal plains are some of the flattest places on Earth. They cover almost a third of the Earth's surface. You could say that the abyssal plains and the oceanic trenches are similar because, when you get to the true abyssal plain, you're thousands of feet below the surface. It is the same with the bottom of an oceanic trench.