Get Elizabeth Lyon's Nonfiction Book Proposals Anybody Can Write.
Your book should be written/rewritten/rewritten again/edited/polished/rewritten -- you get the idea, before you query agents. Have a synopsis ready to go before you query agents. Have a proposal ready before you query agents. READ AND ABSORB: the Query Shark and Miss Snark stuff. Read agent's web pages (Janet Reid, Nathan Bransford, Bookends, LLC, etc.). Google "literary agent blog."
Be prepared to submit query/proposal/manuscript electronically and by snail mail.
If--IF!!!--you do find a willing publisher, be prepared for a title change.
Check out Behler Publishing's web pages and blog, re: queries, writing
and the publishing business.
It sounds like you need to learn A LOT more about the business. That's not meant to be a snarky comment. No one's born knowing this stuff. Don't expect to be plucked from behind a drugstore counter like Lana Turner.