Here are some differences between a writers notebook and a blog.
Writers notebooks handwritten and private. You can write about anything, because in a writers notebook anythings OK. When you post on a blog it is over electronics, and it is public and open to the world. You can not comment on a writers notebook; meanwhile you can comment on a blog-post. The purpose is to express yourself, and grow as a writer. The purpose of a blog is to engage with different audiences.
Those are all the differences I could think of… If you have some please comment them below!