The "where to" is really up to you--and which market your story is geared toward.

You can get an idea of which markets here or here. Good luck.

Here are some general manuscript formatting guidelines although, as IB says, check the format requirements for the specific market to which you submit.
http://www.sfwriter.com/mschklst.htm

Markets generally advise that you should read enough issues to understand the kind of stories they like--it's almost useless advice, really, because they're always looking for something different in order to retain readers' interest and avoid producing issues that are same-ole, same-ole.

For short stories you don't need a summary, just a simple cover letter something like this will do. (I copied it pretty much from an earlier post by KDW.) If you're submitting to a market in the country you live in, a simple stamped addressed envelope is sufficient.

quote:

---

Dear Sir,
Please consider my previously unpublished manuscript "The Story" for publication in Analog. It's science fiction, about 5000 words.

I enclose an addressed envelope for your reply, together with an International Reply Coupon. Please dispose of the manuscript if you do not want it.

Thanks for your time and consideration.

Yours sincerely,

---

Some simple rules: submit the story to just one market at a time, and only submit one story at a time to a specific market. Some markets like paper subs, some electronic, some either. Check their websites for "author guidelines" or such.

Now, if you'd like to run your story by some Hatrackers for a final spit 'n polish, you could try the Ready for Market challenge or Sub-Machine. (Damn, I wish I had thought of that title.)

Finally, the other answer to your "where to go next" question is, of course, write another!

Ah, that brings back memories. I never submitted Story Number One anywhere---it came to just two thousand words, and the markets of the day I was willing to consider all had their lower word length limit at twenty-five hundred words or so. By the time I might've submitted it elsewhere, I realized it was no good and I was doing better work. Story Number Two was my first submission---but that was only a month and a half later. Sixty-eight hundred words, a good length.

(Of course I also later realized Story Number Two---and everything I wrote up through Story Number, oh, One Hundred Seventy Three---were pretty bad. But after that, I thought most of 'em could've been published, right aside some of the garbage they did publish.)