Demons exist. They are spirit beings. They exist in the world. Demons are fallen angels. They are fallen angels because they were cast down from heaven. When Lucifer and some of the angels rebelled against God, the Almighty God cast them down. These evil spirits are everywhere. They are roaming the surface of the earth because they have been cast out of their natural home.
When angels rebelled against the order of God, God cast them out. We have heard about Lucifer who took almost one third of the angels in heaven and conspired against the Almighty God. Because of this action of rebellion, the Lord cast down those angels.
Jude 1:6 (KJV) And the angels which kept not their first estate, but left their own habitation, he hath reserved in everlasting chains under darkness unto the judgment of the great day.
Genesis 6:4 (KJV) There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare children to them, the same became mighty men which were of old, men of renown.
Also, we have heard of those sons of God who came in unto the daughters of men and produced giants. Those sons of God were the angels. Those angels are the demons who are causing all the evil in the world. We must be careful because these evil ones have nothing good for humanity. Their purpose and their aim is to destroy us.
The evil spirits are on earth. Some people are confused whether they are in hell. They are not in hell yet because their time has not come yet. That was the response of some of the demons which the Lord Jesus Christ was casting away. They asked whether he had come to torment them before time.
Evil spirits are real and we need the Holy Spirit in us