How do I actually talk to my mother about my sexual abuse from my father?

This is a huge step and one that will impact the lives of others. Because there are many unknown factors that I don't know, I would suggest you first getting counseling and when you tell your mom, make sure you both are in a safe space and that mom has the support she needs to process the information.

This is touchy, depends on the age of person, the relationship with the mother and the extent of the abuse. To many factors for a general question

It would be best to talk to someone else first such as counsellor or doctor before talking to your mother; to get some guidance or help. Do it in a safe and private place with your mother and tell her it makes you uncomfortable. Discuss what you will do about it and get police help if need be.

What you need to do is just ask her to speak privately, you could leave your home and go somewhere else if that makes you feel more comfortable. But the point is that you need to get her to understand that it is important. You can slowly bring it up by how for years there has been something that has been going on, and explain to her how difficult it is to admit it. That could make it easier on you. But when you do say it, don’t hold back. Get everything off your chest. Scream, cry, hug, the first impulse that you have. If you can trust you’re mother, then she will understand, you just have to have faith that she can take it. It won’t be easy to hear, but it will need to be heard.