How to Become a Published Writer, Step 1:
Write.
Yeah, I know, it’s an obvious step. But it’s a fairly important one, at least in my humble opinion. Except, of course, if you (yes, YOU; I am speaking to YOU specifically, so pay attention!) plan to write non-fiction, where it is in fact acceptable to merely propose a book rather than writing it before trying to sell it – but you’d better at least have some credentials behind you if you go that route. “Hi, I’m Bob the Janitor, and I want to write a book about quantum thermodynamics” is just not gonna be taken seriously as a proposal. So let’s assume you’re trying to publish either a fictional work or a non-fiction book that you plan to actually write ahead of time.
Pick out a word processor. Just about anything more feature-rich than the Wordpad that comes free with Windows will do, and there’s no need for any fancy writing software (with the possible exception of specialized play- and screenplay-writing applications, and for advice on that you’ll need to look elsewhere). I bounce back and forth between Microsoft Word
Other resources you may need for research, inspiration, etc. tend to be specific to your project and/or personality, so I won’t touch on those much except to say this: Dictionary.com and Thesaurus.com are your friends. Nay, not friends; rather, they are your humble servants; slaves, if you will, ready to instantly sate your deepest needs at a moment’s notice. (Yes, I know what you’re thinking, and you should be ashamed of yourself! Besides, there are better sites for that sort of thing, I’m sure.)
Well, you’re all set. Go write that novel.
I’ll wait.