The publishing house they belong to and their literary agent, are responsible for the finances of the book. The author writes the book, writes the query letter, gets an agent, and bugs publishers until they're accepted.
How much they are paid is based upon the public interest -- whether or not people are buying their book. (Royalties)
If you only want to become a writer for the money, then you're going to find this a gruesome business -- it's something you should feel very passionate about. If you're simply concerned about having a career that is going provide you the finance your life is in need of: Writing is usually a second job. Writers might have another writing job, like blood sucking journalism.. or they could be a doctor, psychologist, teacher, etc. It doesn't really matter, but being an author you need another job to fall back on.
An author's paycheck is only as big as his/her's success. So, if creating stories is something you love dong, then do that. Maybe someday it will payoff. Just don't depend your life on it. Keep writing, and work on grammar/spelling every day.