How the witches want to appear and not in the play?

The witches in Macbeth are supposed to be evil. Elizabethans liked that sort of thing. They were flat characters intent on doing harm as far as their "powers" would let them. They always appeared in darkness near a heath during some kind of storm. Darkness was their modus operandi (method of doing things) so everything they said and did followed this. They also meant to appear prophetic with some dark metaphysical knowledge which, against the audience's better judgment, Macbeth relies upon.

They don't want to appear powerless or afraid. They use the power of suggestion combined with chants and riddles to entice Macbeth. They always appear in groups.