There is much folk lore and tradition that has built up around the term Satan and Beelzebub. Some of it true and some of it not. The biblical teaching, however, is quite clear.
Very little is said about Satan in the Old Testament. Where he is mentioned, he is always subject to God (Job 1-2) and always opposed to man’s best interest. In the New Testament, Satan and Beelzebub are used synonomously and seen as the evil ruler of all that is against God. Christians are warned to always be on their guard against him, using the armour of God, and particularly the Word of God, to oppose him. He is seen as a constant cunning enemy of Christ against whom Christian are always in battle.
However the New Testament is also clear about his power and fate. Satan is, since the cross, a defeated enemy, destines for the destruction that comes on the last days. He is still powerful, able to tempt people and lead them astray but Christians are no longer under his control and are able to stand up to him.
Where Satan comes from is unclear from the bible. Several theories suggest a fallen angel but this is only speculation.
As a Christian we are to fight Satan but not bee scared of him.