Demons are real. The Bible says they are and I believe what the Bible says is true. Demons can only inhabit those who are not protected by the Holy Spirit. When you accept Jesus as your Lord and Saviour and have a real relationship with Him, no demon can possess you. They can tempt you to do wrong or possess other people or animals who can then hurt you physically but they cannot possess you if you are saved. The only way you can hurt a demon is with the Word of God. When you speak the Word of God to a demon, it drives the demon away. They cannot stand the light of the Truth. When a demon tempts you (which is the main way they try to hurt us), resist him by citing scripture from the Bible with confidence. This is why it is so important to memorise scripture from the Bible. When Jesus was in the wilderness for forty days, he drove Lucifer himself away simply by refusing to do what he wanted and by quoting scripture with authority. Jesus told His disciples that they coud do everything He did and more if they would only believe and trust in Him. If you remember nothing else, remember these verses and quote them at the demons with confidence:

"Greater is He that is in me than he that is in the world"

"I can do all things through Christ who strenghtens me"

"I am with you always, even to the end of the earth"

"Into Your hands, Father, I commend my spirit"

"The Lord is my shepherd, I shall not want. He makes me lie down in green pastures. He restores my soul. He leads me along the path of righteousness for His name's sake. Surely goodness and mercy shall follow me all the days of my life and I shall dwell in the house of the Lord forever"

"Our Father who is in Heaven, praised (or hallowed) be Your Name. Your Kingdom come, Your will be done on Earth as it is in Heaven. Give me this day my daily bread and forgive me my sins as I forgive those who sin against me. Lead me not into temptation, but deliver me from evil. For Yours is the kingdom, the glory and the power forever. Amen"

If you remember these, and better yet, read the Bible on a regular basis, and most importantly Believe what these words say, then you can fight back against any demon because the Holy Spirit will be with you and will fight for you.