How does forgiveness and reconciliation work?

I'm confused about forgiveness. So, no one owes you forgiveness, not even your parents. (What about when your a kid though?) If someone doesn't forgive you, what does that mean for your relationship? I guess I'm not sure how to continue a relationship if there is unforgiveness between 2 people. So if you apologize and the person can't forgive you, how do you continue that relationship? I also know people say "Don't ever do it again" But there are some things you're probably going to do again and it takes work to get better. Not just a one time, never doing it again. TL;DR In short, how does forgiveness work in relationships? How does it affect if you have a relationship with someone or not?