your mom was a witch, she was one of the best friends of lily, harry potter's mom, your mom died too, when you were 9 years old and your das was a muggle, a drunk muggle. he hated you and he abuse you. you got the Hogwarts letter when you were 10 years old but your dad didnt let you learn there, he didn't let you learn at all, he kept you and the house all the time and kept hit you. every year you would get the letter again and again until the 4th year, you decided to go. ofc you didn't knew how but we will deal with this later, first you need to leave the house.