Lens hoods are primarily designed to prevent unwanted stray light from entering the lens by extending and shading the end of the lens. In addition, since the end of the lens is extended, you also get the added benefit of some extra protection from accidental impact.

Dedicated lens hoods are designed to match the specific focal length of the lens it was designed for.

The Nikon HN-23's inner surface nearest your lens' filter thread is beveled and does not directly accept a 62mm lens cap.  However, a 77mm lenscap fits nicely into the inside diameter of the front of the hood.