A prism is a shape with a constant cross section, in other words the cross-section looks the same anywhere along the length of the solid (examples: cylinder, cuboid). 

The volume of a prism = the area of the cross-section × the length. So, for example, the volume of a cylinder = pr² × length.

• area of a triangle = half * base * height so the volume of a triangular prism is half*base*height*length

• area of a circle = pr² (r is the radius of the circle) so volume =pr²l

• area of a parallelogram = base × height so volume =base*height*length as for a rectangle

• area of a trapezium = half × (sum of the parallel sides) × the distance between them [ 1/2(a+b)d ] so volume of a trapezoidal prism is 1/2(a+b)dl

There are some shapes that must have their own formula for volume since cross section of a sphere for example, doesn't make much sense.

Sphere: Volume: 4/3pr³
Pyramid: Volume = 1/3 × area of base × perpendicular height (=1/3pr²h for a cone).