San Diego, California
Agents and/or publishers are likely to have different submission guidelines. Do some online research to see what genres publishers will accept; go to the chosen website and follow their particular guidelines for submission to the letter, or they may not look at it. Remember, most have lots of submissions to sift through daily and you want to get their attention, not deflect it.
Some publishers will only accept work through an agent; others will accept unsolicited submissions by way of an email, by either a proposal/summary or your manuscript.
Therefore, unless you are self-publishing, you will need to prepare a book proposal. If you are unsure of how to proceed, you can contact me to request a list of guidelines I have available for both fiction and non-fiction, or research it online. It is important that you the author write this because it should be written from your perspective; only you know what content is most important to your message.
You may also need a query letter (you can research the particulars online).
Both agents and traditional publishers will charge fees (normally a percentage). In most cases, you sign a contract, usually giving over control of your manuscript, and retain little of the profit, hoping to make it up in volume. This can happen, but is often a rarity, not the rule. Be sure to specify and negotiate what is important to you in the contract and read the fine print.
Jami Lynn Sands