I've found writing advice on how to start a story to be very...general. And, it's not because they are lazy or they just want to look legit. There is a very good reason they are being general (which not many of them actually address). That is, there is no true method for you to write your story. The only thing some experienced writer can do to give advice on how to start a new story is say how they start a new story. I recently started a new story. So let me give me as an example on two ways you can start a new story.
I tried to start writing a new story after finishing two novels simultaneously. I've been writing for almost ten years. Through commentary on 2019 me, let 2020 me show you what was not working and why I failed this new project.
Let's be very real here. There is no story that's practically perfect in every way like Mary Poppins. At least, not from the first draft. I can guarantee that J. K. Rowling had to edit Harry Potter a bazillion times to get it to where it is now. First drafts are always just you, the writer, splurging all your ideas out on paper. It's very raw. Editing is when you cook it up and add seasoning. Suddenly that got delicious 😛
World building is the base of your fantasy novel. Any amount of imagined something will need to be built to ensure your world will not topple down if someone blew on it. You need to make a steady world and world-building websites might not always give you all the resources you need. Sometimes you have to figure some stuff out yourself and if you haven't gotten there yet, don't worry, I have you covered.