How has Shakespeare represented the witches?(e.g. language directions, settings, descriptions, etc.)
Concerning Shakespeare's Macbeth and the witches, I don't know what "language directions" are. And not much is given in the drama concerning physical descriptions of the witches, which is pretty normal for a play. I can point out two important aspects of the witches that are relevant to your question, though.
Concerning setting, the witches open the play in thunder. They later meet Macbeth and Banquo on a heath. A heath is a wild, unkempt plain, usually associated with mystery and desolation. And the storm of the first few scenes is foul and fair. The witches' environment mirrors the state of political affairs in Scotland, and the witches, of course, contribute to the unnatural state of affairs.
Concerning description, the witches are androgynous: they appear to be women but have beards. They appear to be women but also appear to be other worldly. These opposites, too, mirror the fair is foul and the foul is fair of the play. Virtually no one is as he/she appears: the traitors appear to be loyal thanes to Duncan, but are not; Macbeth appears to be loyal, but is not; Lady Macbeth wants to be a man; Macduff is loyal, but is suspected of not being so by Malcolm.
The witches introduce and contribute to themes and imagery, and serve as catalyst for the plot. Their environment and their appearances play a role in doing so.