I'm 11 years old and I love creative writing. I'm writing a novel and I am trying to do it on my own. What is the best world building tool? What is the best writing platform? How do I find a writing partner?

It is wonderful that you have a passion for creative writing, which is most important. It seems like you are still developing your novel. As for the world-building of your book, you can make several lists of elements you want to include in your story and fictional world. There are many online writing tools for worldbuilding such as World Anvil and Persona. You don't need to rush the process of writing a novel. For one thing, your book does not need to be published by the time you are eighteen years old. With time, patience, and practice, your writing will greatly improve. A writing partner can be really helpful for you and they can be found at school or through a writing workshop.