What does it mean to forgive exactly?

God says to forgive or you won’t be forgiven (Matthew 6:14-15) so if someone murder your entire family or did something to ruin your life obviously you’re not gonna forgive them. I’ve heard people say “Jesus went through it so should we” and I still don’t see how that fair or right. I’m not saying to go hunt down or hurt that person but obviously I’m gonna be bitter towards them.