They plan on doing this by using their supernatural power which includes charms ,and spells. they also plan on achieving this by prophecies, they revealed things to macbeth which made him think he was untouchable and invisible when the war came. As a result of this Macbeth was lead to his downfall instead of his success. The witches goal could be seen as a concept of deception considering the fact that they were able to deceive macbeth for so long into believing every word that they told him from day one, about him becoming king which made him to start considering killing duncan and taking over the kingdom. Not to mention they were able to convince him that he was untouchable and anyone born by a woman couldn't harm him with regards to this he felt safe and comforted by the witches