I read these books years ago but never got to finish them. I am trying to figure out the name of the books but cannot remember at all. I will try to describe them as detailed as possible but it has been years and some information might be a little off. I read these in middle school if that helps. The series was probably 8+ books.
The first few books are about a young kid that somehow finds a mysterious book that contains a like magical passage that when read gives the reader of this passage access to like the magical world. He eventually finds other people like him and practices with them. A specific scene that i remember is that after school him and one of his female friends that happened to also have some magical powers go to the forest, cast some sort of spell that makes it so that people can't see whats going on in the area the spell is cast on. This way they can go about doing magic and practicing without having to worry about other people seeing what they were doing.
Later on in the books his little sister finds the book and reads the passage by accident. She also gets powers and (I believe it affects everyone a little different because her magical powers were different) she was given a mind kind of like a computer and was able to process information really fast. There's a part in the book where she is communicating via typing things out because she could do it way faster than speaking to her.