Revelation 12:4,9 (NIV)
4 Its tail swept a third of the stars out of the sky and flung them to the earth. The dragon stood in front of the woman who was about to give birth, so that it might devour her child the moment he was born.
9 The great dragon was hurled down—that ancient serpent called the devil, or Satan, who leads the whole world astray. He was hurled to the earth, and his angels with him.
The devil is real and demons are real. We can't see them because they are spirits. We can only see the fruit/action/manifestation of their work which they initiated by planting thoughts in the minds of people who whether knowingly or unknowingly acted on the thought. So with a third of the angels fallen to earth... this lets us know that there are so many we can not even count. They are dark soldiers. Every soldier has a specialty. They are well organized out of sight, but the end result by their coordinated effort/warfare looks like chaos and confusion...strife, envy, hatred, dissensions, manipulation/witchcraft, sexual immorality, and so much more as identified by the Apostle Paul in Galatians 5:19-21. It is basically rebellion that distracts people from searching for what is true. Every demon has a specialty. Just like if the US wants to bomb something it is not going to send the marines in... it will send the Air Force. Or when it was going to get Bin Laden... it sent in the Navy Seals... not the Air Force. Even within a team of Navy Seals... each Seal has a special function. And this is so in the spirit realm where there is a spirit behind everything we see people do. This is why Jesus says in Matthew 7:16 that you will recognize them by their fruit. Fruit is an outward thing to be seen by the plain eye. But if we are not walking by faith and not by sight... we won't recognize what we see.
There is a spirit behind everything. There are good angels and bad angels. The good angels are led by God. The bad angels are called demons and they are led by satan. Every action in the earth is led by a thought. The key is to know what spirit is behind the thought. This gets at the motive. A Godly spirit will demonstrate what is written in Galatians 5:22-26. This is called the fruit of (God's) the spirit. And those who belong to him will begin to show this fruit. It is a process for the believer. And even in this state, we still have to guard our ears and eyes against images and sound that try to corrupt the mind. Everything is spiritual folks.
The person who begins to understand this is wise. You are allowing Proverbs 3:5-6 to truly be the GPS for how you walk, how you interact with people, who to trust and who not to trust. The deeper we go into the word of God and he gives us an understanding/insight... the less desirable this place becomes. I will use the analogy of that attractive person who caught your eye. Yes that person looked good until that person opened his or her mouth. The more you got to know the person, the less desirable that person became to you. And so it is like this world. It looked good on the surface, but when you got to see it for what it really is... it was not attractive at all.
Then we will fully understand Ephesians 6:1-18 and 2 Corinthians 10:4-5!
The enemy's effort is to distract you from your focus on God completely. A complete focus on God is worship (Matthew 6:33). This is what Jesus was showing us.It is in our worship which includes prayer/communication/talking to God and listening to him.. that we will see we have dominion/authority/power over every effort of the enemy.