Also known as, "How do I format this thing?"
One thing some authors overlook as they're preparing a submission is how the publisher or agent wants things to be formatted. Especially with small presses and e-publishers, though even with larger publishers and agents, there is sometimes a specific requirement for font, margins, etc. to make the submission easier to read and/or to make it easier to format for the final released version.
This is another piece of information you may be able to find in a publisher's or agent's submissions guidelines. For example, in looking at a couple of my publishers, one says essentially "We don't care how it's formatted as long as we can read it." Another requires Times New Roman 12-point font, one-inch margins, double-spaced, first line auto-indented .3, no tabs, no double space after a period, no double space at the end of a paragraph, use four asterisks for scene breaks, put chapter headings in bold 14-point font, centered.
Those are only two examples, and you can see there's a pretty wide range between them.
Just as with any other piece of the submissions guidelines, if a publisher or agent lists a specific way to format your manuscript, it's important to follow that guideline. If you use Courier font instead of Times New Roman, it might not mean the end of your chances with that company/agency, but they might question how you'll handle edits and instructions if you can't follow their rules. If there is no formatting guideline, you usually won't go wrong with an easily-read font such as Courier or Times New Roman, double-spaced, with one-inch margins, but you also probably won't go wrong if you email for clarification. (I feel like I'm saying that a lot in these posts...Truthfully, most publishers and agents don't mind answering questions, and you shouldn't feel awkward about asking them.)