I want to submit to Fantasy Magazine and their submission system has a field open where I should enter a cover letter.
Now, that field is not marked with an asterisk so it is not mandatory but I'd still like to have one.

I googled for tutorials on cover letters but I still am not sure how I should approach this.

Can I get a little help here from you guys?

Here's what I would do:

Dear So and So,

[Quick 4-5 sentence summary of the plot of your story. The shorter the story, the shorter the summary, generally speaking. Make it interesting, though. Lead with a hook.]

[Paragraph about yourself: keep it professional. What qualifies you to write, and specifically what qualifies you for this story. If you have any previously published credits, you'd put them here.]

Thank you for your consideration.

Sincerely

Your name

Check out this web site for what literary agent Nathan Bransford calls "Query Mad Libs".

http://blog.nathanbransford.com/2008/03/query-letter-mad-lib.html

I think it will help, even with a cover letter.

Your greatest resource might just be this forum. Write what you think is a good cover and post it. I promise, people will respond.

Good luck! My fingers are crossed for you!

Dear Editor's Name (not just "Dear Editor"--find out who the editor is and use his or her name),

Here is my story, TITLE GOES HERE, for your consideration. This is not a simultaneous submission.

I have had [OTHER STORY TITLE] published in [FAMOUS MAGAZINE TITLE], and a novel series, [TITLE OF FIRST], [TITLE OF SECOND], and [TITLE OF THIRD], published by Big Name Publisher].

I look forward to hearing from you (if you've enclosed a SASE, you can say, "using the enclosed SASE" or if you haven't you can say "through email"--enclose a SASE if you want your manuscript back. If you don't need the manuscript returned, you can say that the manuscript may be recycled).

Sincerely,
Your Name

The first sentence in the first paragraph above is necessary because it connects you and your contact information (name, address, email address, phone number) with the manuscript by the story title--in case there is a mishap and a bunch of manuscripts tumble to the floor and get scattered and mixed up. (Even the second sentence in the first paragraph isn't really necessary. If it IS a simultaneous submission, then that information IS necessary, but most publishers will tell you in the guidelines whether they will consider simultaneous submissions, and if they do, they will ask that you tell them if it is one; otherwise, it had better not be.)

The publishing credits (second paragraph above) are not necessary if you don't have any publishing credits--and only list the four of five most recent professional credits, not any semi-pro or small press credits.

The third paragraph is nice, but not necessary. After all, if you've enclosed a SASE (because the guidelines say to include one and/or because you want the manuscript returned) or if you've given them your email address, they know what to do with those things.

That first sentence of the first paragraph is all you need to put, really.

I think I got it, but there is one more issue, namely:

http://www.fantasy-magazine.com/about-2/editors-and-staff/

"Dear (Editor)

Please find enclosed a story for your consideratoin.

I have sold stories to a range of magazines, including X, Y and Z.

I look forward to hearing from you,

Brian Dolton"

Without sales, I'd simply omit that middle paragraph (and note that I NEVER mention more than three or four markets, and always the ones that are the most well-known/prestigious and ideally similar to the market I'm subbing to).

General form, as I understand it, is always to address the letter to the chief editor, even if you know someone else will be reading it. So though Doug Cohen is the first stage reader at RoF, the mail would be addressed to Shawna. So in Fantasy's case, it would be Sean, I believe, though you could put "Dear Sean and Cat" (when I sold to Fantasy, all my dealings were with Cat, but I know things have changed a bit since then).