How are hover boards made?

They are purely fiction. The actor Michael J. Fox is first seen riding one in the movie Back to the Future, but the 'hovering' was just a movie special effect, as it was in other hovering boards in some later movies. Basically it is a normal skate board without wheels. Hover boards have never been made - and could not be made - in real life, since a real hovercraft effect could only be created by something much larger and much more elaborate (and engine-driven) than a simple wooden plank.