Have you ever experienced a presence of evil? Have you been around someone who seems to exude a dark, oppressive, malevolent force? Maybe you've had the experience of being out in public, caught someone's eye and instantly there was a jolt--a sudden slam of sheer violence and hatred hitting you via eye contact. . . . Or, you have entered a building or home where there was an immediate sensation of danger--a general foreboding . . . pressing on you with some unseen, heavy antagonism. . . .
It is always there, to some degree, when you engage with the world; when you consume various entertainments--music, t.v. shows, movies, news reports. . . . There is such a barrage of filth, perversity, and overall blaspheming spirit included throughout the presentations . . . the Spirit within you is constantly being grieved to some degree.
Or, let's hope so. Otherwise, it is a clear sign of danger when you can consume worldly media and all you get is entertained, amused, titillated, with no offense taken.
I would not dare claim a complete or perfect definition or understanding of evil. There is a mystery to it; "the mystery of iniquity" is referred to in 2Thessalonians 2:7.
But I dare suggest, along with others, that it is not a thing. It is a negation--the absence of good revealed in the "withholding" of God's Spirit. I also don't believe it is in itself a force. Beings who hate God, however, and thus exist in the absence of good, use and employ existing forces . . . to, in a sense, amplify the negation, and so derive a certain destructive evil "power".
What you are experiencing then, when you come across that dark, threatening "presence" of evil, is simply the absence of God, of good. . . . The more God is absent, the more the "power" of evil is exhibited and felt.
The more you neglect God . . . ie., by not praying, reading scripture, seeking His will, pleasing the Spirit, fellowshipping with other believers, reading and thinking on Spiritual issues etc., the more you are leaving open that space wherein "evil" can enter. Evil is the absence of good/God. When God is not there, evil is bound to result.
So, the answer always is to dwell on God, focus on God, fill your mind and heart with the good things of God so that evil can find no room to fester and escalate. Where God (Who is Light and Love) is not present, darkness begins to reign, by default, and so do all those things and beings that thrive in the darkness.
If and when you ever start to feel evil "pressing" in. . . . If and when you find yourself oppressed with fear, anxiety . . . and/or other negative, unholy, ungodly emotions and thoughts, it likely means that you have been neglecting God. You have not kept His presence and purposes foremost in your soul, but have there instead a negation of Him, lack of Him . . . so that evil/darkness necessarily results. . . .
Where God ISN'T (so-to-speak) evil IS. Of course, we know that God is everywhere, but He has made it so that in this realm of creation we can experience something like an absence of His presence--a lack of His "active" Spirit. And, indeed, this involves His very purpose in all this: the divine demonstration of what existence is like with versus without Him "in it."
The danger in blithely consuming so much of the world's constant barrage of the various avenues of its media . . . is that we are "filled" . . . with the absence of God, of good. The result is a pervasive privation of holiness, and therein the enemies of God enter and make their home.
The answer--the antidote . . . is to reclaim your "space" by filling it with God and Godly matters. It takes action, effort, impetus! If you merely "go with the flow" and accede passively to all that the world is washing over you, without deliberately seeking His Spirit, in His "absence" . . . then evil spreads its darkness and the entities who dwell in it become your fellow residents.
Darkness "hates" the Light. Evil thrives where God/good is NOT.
During this age/space and time, where God has turned over . . . for a season . . . the world to the rule of said darkness . . . the Child of Light is necessarily engaged in battle. It is a fight for the light--a struggle, a wrestling. . . . Passivity and acquiescence to the "ways of the world" is the way of evil. It is the "lukewarmness" that Jesus plainly detested.
Resistance . . . against the pull of negation . . . is Godly--is a Godward action.
Again, remember that evil . . . is what results from the absence of God. It is not a thing. It is not an equally opposing force to good (as the occultists deceptively promote.) It is just what happens when God withholds the fullness of His Spirit. as when men and women turn AWAY from Him, rejecting His will. The moment a being "looks" away from God, to him or her self . . . or to another creature or part of creation . . . valuing that thing or being MORE than God . . . evil ensues as a "natural" by-product--a necessary result. For nothing can exist in goodness independent and apart from the source of ALL good--from He Who IS what "good" is. . . .
You can NEVER lose--regardless of present circumstances/temporary results--so long as you are praising God in ALL things, keeping His Spirit and purposes foremost in your mind and heart. Darkness must depart. Do not allow "it" to take root, to push out Jesus. . . . Fill yourself with God, with His goodness . . . and evil flees.