This one is pretty simple. To start, you need something to put your story on. You can go the classic route and grab a pen and a notebook, and start scribbling away. Or you can type your story on a computer. The latter may be the safer route, because you can backup your work and create multiple copies quickly.
Whether you're writing a fiction or non-fiction book, you need to do some research on your subject. For non-fiction books, you obviously need to have your facts straight and your details in order. For fictional stories, you need to know what you're talking about, or else your story won't be very believable.
Everybody needs somewhere to do their writing. Most important is to find somewhere that makes you comfortable and doesn't provide any distractions from your writing. Some people prefer quiet, solitary workspaces such as a home office, somewhere they can have peace and quiet to concentrate on their work. Others prefer somewhere they can interact with other people, such as a coffee house. Wherever you choose, just make sure it's a place that allows you to get comfortable and focus on your writing.
There is one book that every writer should have, be they a poet, fiction writer, screenwriter, journalist or whatever. That book is "The Elements of Style" by William Strunk, Jr. and E. B. White. It is the most important guide on style and usage of the English language, something no writer should be without.
Other helpful tools are a dictionary, a thesaurus, and whatever research materials are pertinent to the subject you are writing about. These things will help you keep working without getting stalled.