Find the area of one of the sides of the prism. Measure the length and width of one side of the prism and multiply them, or, if the prism is something like a cylinder, square the radius and multiply it with pi.
Find the height of the object -- do this for squares, cylinders, rectangles and all prisms -- and multiply it with the number you got in the previous step.
Multiply the height and either the width or length, and multiply that by the remaining side's value as an alternate way of finding the volume of prisms like squares and rectangles. When dealing with a shape like a rectangle, it doesn't matter which two numbers you start with because you'll eventually multiply all three.
Find the area of the base of the pyramid. If the pyramid has four sides, the base will have four sides; multiply the values of two adjacent sides. If it has three sides and the base is a triangle, choose one edge of that triangle to be the base, multiply it by the height -- the length of the perpendicular line that stretches from the base line to the apex of the top point of the triangle -- and multiply all that by 1/2. Whatever shape the base of the pyramid is, use the formula you would normally use to find that shape's area. Note the base of a pyramid is never round; that would be a cone, not a pyramid.
Multiply the area of the base by the height of the pyramid. The height is, like the height of a triangle, the length of the perpendicular line that stretches from the bottom of the pyramid right under the top point, all the way up to that top point.
Multiply the value from the previous step by 1/3.