When God created the heaven and the earth all of the angels sang together, and all the sons of God shouted for joy (Job 38:7). But then, some of the angels, led by Lucifer  (also called Satan) rebelled against God and they were cast out of heaven (Isaiah 14:12; Ezekiel 28:16; Jude 6:1; Revelation 12:7-9). These angels, Satan and the others are also known as fallen angels and/or demons and evil spirits. The Bible calls Satan and the other demons “rulers of the darkness of this world” (Ephesians 6:12).
It is important to know that Satan is not the opposite of God because only God is all powerful and Satan is lower than God in that he is a created and limited spiritual being. Satan needs God’s permission to do anything and everything. Satan cannot read our thoughts (Isaiah 40:28; 1 Kings 8:39; Psalm 94:11). Satan does not know the future (Isaiah 46:9-10). And above all, Satan is a coward (James 4:7). But even though he and his angels fell from heaven, God still allows them to do certain things. Here are just 15 things that Satan and evil spirits can do.
1) Satan is Permitted to Impair the Righteous
Job 1:12 And the LORD said unto Satan, Behold, all that he hath is in thy power; only upon himself put not forth thine hand. So Satan went forth from the presence of the LORD.
2) Satan is Permitted to Have Dominion Over Sinners
Acts 26:18 To open their eyes, and to turn them from darkness to light, and from the power of Satan unto God, that they may receive forgiveness of sins, and inheritance among them which are sanctified by faith that is in me.
3) Satan is Permitted to Blind Sinners
2 Corinthians 4:3–4 But if our gospel be hid, it is hid to them that are lost: In whom the god of this world hath blinded the minds of them which believe not, lest the light of the glorious gospel of Christ, who is the image of God, should shine unto them.
4) Satan is Permitted to Contend with Sinners
Ephesians 6:12 For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places.
5) Satan is Permitted to Tempt Believers
Genesis 3:4–5 And the serpent said unto the woman, Ye shall not surely die: For God doth know that in the day ye eat thereof, then your eyes shall be opened, and ye shall be as gods, knowing good and evil.
6) Satan is Permitted to Disparage the Saints
Job 1:9–11 Then Satan answered the LORD, and said, Doth Job fear God for nought? Hast not thou made an hedge about him, and about his house, and about all that he hath on every side? thou hast blessed the work of his hands, and his substance is increased in the land. But put forth thine hand now, and touch all that he hath, and he will curse thee to thy face.
7) Satan is Permitted to Administer Disease Upon the Saints
Job 2:7 So went Satan forth from the presence of the LORD, and smote Job with sore boils from the sole of his foot unto his crown.
8) Satan is Permitted to Fight Against the Righteous
Zechariah 3:1 And he shewed me Joshua the high priest standing before the angel of the LORD, and Satan standing at his right hand to resist him.
9) Satan was Permitted to Tempt Jesus
Matthew 4:1 Then was Jesus led up of the Spirit into the wilderness to be tempted of the devil.
10) Evil Spirits are Permitted to Inhabit the Bodies of Unbelievers
Mark 5:1–9 And they came over unto the other side of the sea, into the country of the Gadarenes. And when he was come out of the ship, immediately there met him out of the tombs a man with an unclean spirit, Who had his dwelling among the tombs; and no man could bind him, no, not with chains: Because that he had been often bound with fetters and chains, and the chains had been plucked asunder by him, and the fetters broken in pieces: neither could any man tame him. And always, night and day, he was in the mountains, and in the tombs, crying, and cutting himself with stones. But when he saw Jesus afar off, he ran and worshipped him, And cried with a loud voice, and said, What have I to do with thee, Jesus, thou Son of the most high God? I adjure thee by God, that thou torment me not. For he said unto him, Come out of the man, thou unclean spirit. And he asked him, What is thy name? And he answered, saying, My name is Legion: for we are many.
11) God Permits Satan to be Disguised
2 Corinthians 11:14 And no marvel; for Satan himself is transformed into an angel of light.
12) Satan is Permitted to Confuse Men From Understanding the Gospel
Matthew 13:19 When any one heareth the word of the kingdom, and understandeth it not, then cometh the wicked one, and catcheth away that which was sown in his heart. This is he which received seed by the way side.
13) Satan Can Cause Men to Lie
John 8:44 Ye are of your father the devil, and the lusts of your father ye will do. He was a murderer from the beginning, and abode not in the truth, because there is no truth in him. When he speaketh a lie, he speaketh of his own: for he is a liar, and the father of it.
14) Satan Can Prompt A Man to Betray the Lord
John 13:2–4 And supper being ended, the devil having now put into the heart of Judas Iscariot, Simon’s son, to betray him; Jesus knowing that the Father had given all things into his hands, and that he was come from God, and went to God; He riseth from supper, and laid aside his garments; and took a towel, and girded himself.
15) Demons Will Work Miracles
Revelation 16:13–14 And I saw three unclean spirits like frogs come out of the mouth of the dragon, and out of the mouth of the beast, and out of the mouth of the false prophet. For they are the spirits of devils, working miracles, which go forth unto the kings of the earth and of the whole world, to gather them to the battle of that great day of God Almighty.
While it is impossible for a believer to be possessed internally by a demon (1 Peter 1:5, 1 John 4:4, 1 John 5:8), Satan and his fallen angels can still cause all sorts of problems. He is walking around the earth seeking whom he may devour. And for this reason, we must be sober and vigilant (1 Peter 5:8).
Read more here: Angels & Demons 
Resource – Scripture quotations are from The Holy Bible, King James Version.