The why is easy. You want to keep a record of the people, companies, theatres etc. that you have sent your work to – or sent a query letter to – so that you don’t:
• Duplicate submissions (which will waste your time and piss the submittees* off)
• Miss submitting to someone you should submit to (which may prevent you from getting published or produced)
I recommend using an Excel worksheet. It’s easy to use and does everything you need it to do. If you have another program that you prefer, use it. There is no one way to do this.
What should your spreadsheet include?

• The name of your work – this can either be a column, or you can have an entire tab devoted to one work.
• The name and title of the person or company or organization you’re submitting to.
• The name of the publishing company, theatre company, publication or whatever organization it is that you are sending to.
• What you’re sending. Is it a query letter? The first ten pages or three chapters? A synopsis? What goes in this column will depend upon what the submittee says he or she wants you to send. You can find this information on the company’s website. Do not ignore it. If a literary agent wants a synopsis and the first five pages, do NOT send the entire novel or nonfiction book because it is so brilliant, so well-written THAT YOU ARE CERTAIN the agent will want to read the entire thing, not just five pages. If the agent likes those pages, he or she will ask to see the entire manuscript. Disregarding instructions is a BIG red flag; you are letting the agent know that you will be difficult to work with. Likewise, if a publisher says they don’t accept unagented work and you don’t have an agent, don’t send to them out of an overabundance of confidence. It will be a wasted effort.
You may NEVER get a response
Sadly, many cells in this column will stay blank. You often won’t hear back from agents or publishers – even those who say they are open to submissions. Accept that fact right now, so you won’t pine away for an acknowledgement that you exist. That you write. Some agents will answer you, but that will almost always take a looooooong time. Agents get a lot of submissions. Don’t think about that. It will only depress and discourage you. If you are determined to be a writer, write and submit. Rinse and repeat. Screw the competition.
If you actually DO get a response-
Keep notes about them. I might write something like: “nice rejection email – it’s in agent folder.” That tells me to check that email I saved the next time I submit a (different) work to that agent. I might use the comments in their email, to remind them that they liked my writing the last time. “I appreciated the positive feedback and constructive criticism you gave me on my novel, ‘Palm Tree Pipe Dreams.’” With that, I am reminding the agent that even though they did not decide to represent me, there was something about my writing that they liked. If an agent absolutely HATED my work (and they will rarely admit to that), I jot that down, too, so that I don’t waste time sending to them in the future.
Other things to keep track of
Make note of things you learn that will save you time and effort going forward. Things like:
• Ms. QPOEIREWPOIU is no longer with this agency.
• This agency is no longer in business.
• This agency says it no longer accepts submissions.
Like that. Information that will help you going forward.
A lot of the above is relevant for fiction, nonfiction, short stories, plays and other creative endeavors. You can also keep a spreadsheet when applying for paid writing assignments or for full- or part-time writing jobs.

