I don't know how to forgive people. How do you do it?

You don't have to. If you find someone hard to forgive, then so be it. Keep the hatred. For example, I'm not an easily offended person, but if someone really pisses me off, or intentionally tries to fcuk me up, I'm going to hate him / her for the rest of my life, though I may not be willing or be able to do anything for revenge.