What is Sin?

Mary • Hi! I`m Mary and I`m a college student. Been with PCOS for 17 years. I like volunteering and playing with my phone.
If you are Christian then you already know what that is. Those pesky nasty things we do to ourselves, others, or God. But when undergoing that process of tempation, at least for me, it's almost like being under a spell. Feelings say "Wow that sounds really good" and you have almost temporary amnesia of what happened the last time you fell for sin. Your brain might not have the energy or the willpower to fight it off sometimes, but when it does you can come out of that spell and say "looks good but pass". Just like our brains can help us, God can give us strength we need to fight our way to being good and holy like He is through the Holy Spirit and the power of grace. 
Another way of avoiding being caught under the spell is not going to the things that cause you to go into temptation in the first place, reading your bible, and having a real concrete   relationship with God, nothing formal or fake about it, just be honest. If you're annoyed or mad at him, tell him about it. If your happy, tell him. If your sad, tell him. If were like me shy by nature and saw God as the scary big guy in the sky who says he loves people, but looks a little unapproachable, start small. God will find His way of opening you up little by little. 
So what is sin? Sin is not necessarily just evil, but the absense of good as well. So not doing bad things is not enough to get to heaven. Faith is accompanied by good works. So go do that bakery volunteer job, donate to your favorite charity, or anything does something for other people. 
So blessings to all of you on your journey towards God!