I have learned through practice that forgiveness is for yourself, not for the one you are forgiving. It really doesn't matter in many cases whether they even know or accept your forgiveness. But YOU have let go of the burden of wishing the past could have been something it simply was not. And the freedom of letting go can be pretty amazing – you will feel lighter and have more choices available to you going forward.
Forgiving the past for being what it is, and forgiving other people for being their imperfect selves, is NOT the same thing as forgetting. It is simply making peace with the event so it does not go on distracting your life with a sense of outrage or regret. It does NOT mean you have to let the offender do whatever it was that harmed you in the first place. It does NOT mean making yourself trust someone who is untrustworthy. It does not even require that you become friendly with the offender.
It DOES usually mean acknowledging that they probably were doing the best they could, within the constraints of the upbringing and education and beliefs and needs they were dealing with, at the time they hurt you.
I have had 60-some years to come to terms with the way my mother raised me. There were so many things lacking in her mothering, and so much rigidity and hyper-control, that I recognized that I was seriously dysfunctional by the time I reached my teens, and I could see how badly my younger sisters had been affected. I honestly hated my mother for many years, and stayed as far away from her as possible. But as my own daughter grew up, I realized I needed to make peace with my past for her benefit, as well as my own. Too much baggage threatened to make some of my parenting choices less healthy than they could have been.
So I have found processes that allow me to forgive the past and most of the problems it had caused me. One way was prayer, and I found the pattern and content of my prayers gradually changing as I gained maturity. One was to learn to nurture myself in the ways that my mom had been unable to provide. That was with a skilled and empathetic physical/emotional therapist.
Another was through a process called The Work, that gives some pretty interesting and effective tools for working with negative feelings about people or situations. You can download the materials for free and try it yourself at this website: http://thework.com/thework-4questions.php. My husband and I have both really enjoyed doing The Work, and have found it extremely helpful.
So, today, I live next door to my mother. I'm available to help her when she needs help, which is occurring more often as she ages. I don't love her exactly, but I recognize all she tried to do for me and feel gratitude that she sacrificed so much. I can be around her for a few hours at a time without hating her or feeling too burdened. But I have very clear boundaries now, which she has learned with some difficulty, and she no longer gets away with the petty games and power trips she used to pull. It's working pretty well!