Wrapping vs. Filling.
Volume is the space inside a 3D shape. Surface Area is the total area of all outer faces.
Archimedes was so proud of proving the volume of a sphere is 2/3 of its cylinder that he requested the diagram be carved on his tombstone.
Prisms: V = BaseArea * Height. Pyramids/Cones: V = (BaseArea * Height) / 3.
In Plain English: Imagine a shape is a hollow container. Volume is how much water fits inside. Surface area is how much paint you need to cover the outside. Volume is 3D (cubic units), Surface Area is 2D (square units).
In The Real World: HVAC Engineering. Calculating the volume of a room to determine how powerful the Air Conditioner needs to be.
Confusing Slant Height (side of a cone) with Vertical Height (straight up the middle). Volume always uses Vertical Height.