A prism is a polyhedron comprising an n-sided polygonal base, a second base which is a translated copy (rigidly moved without rotation) of the first, and n other faces (necessarily all parallelograms) joining corresponding sides of the two bases (called lateral faces).
Hence:
1. if the base of a prism has n sides, then the prism has n lateral sides;
2. by the definition, a prism has 2 equal bases and from the first part it has n lateral faces that together form n+2 faces.