Answer:
The surface area is the size of a 2-dimensional surface of a 3-dimensional object. The unit of measure will be a square unit, such as square inches or square meters or square miles. The volume of an object is the total amount of space contained inside the object, and it is 3-dimensional, so the unit of measure is a cube, or 3-dimensional unit, cubic inches, cubic meters, cubic miles.
Speaking of cubes, think of a cube 1 inch on each side. (This is kind of like a large die, as in one of two dice, only without the dots.) Each edge is 1 inch long. Each face is one square inch in area. It has 6 faces, just like a die, top, bottom, and 4 sides. So the surface area of a 1-inch cube is 6 square inches. The volume of a 1-inch cube is calculated by multiplying length x width x height: 1 inch x 1 inch x 1 inch = 1 cubic inch.