what does the beast represent? how is it used by Jack to control the others? Are there parallels for "the beast" in the real world, the one outside of fiction?

The "beast" represents the boys' internal fear and propensity for evil. Golding felt that human nature is dictated by fear and the fulfillment of primal urges rather than compassion and responsibility. The beast is manifested as an external force in the island. Of course it is Simon that the only threat on the island is themselves, "Maybe there is a beast....maybe it's only us". Jack quickly learns that the existence of a beast can work to his advantage. Jack can give the boys the illusion of protection and thus gain control of the boys. The thematic importance of the beast certainly exists in our own world. Fear is all over the news. Fear sells well and gives polititians power. Consider how certain political parties used fear after 911 to gain political favor from the public.