A pyramid joins all the vertices of its base to a single point. A prism has the same polygonal shape and size at its top as at its base and the vertices of top and base are joined to make the edges.
In a pyramid all but one face is a triangle, and the remaining face is the base. In a prism the base and top are equal polygons and the other faces are rectangles.
The volume of a prism is the area of its base times its height. The volume of a prism is 1/3 of the vertical height times the base area.