Simply replace the unfilled areas such as "" and "[date]" with your information.
Dear [name of editor],
Enclosed please find [title of work] a [number of words in work] word, [genre of work] [short story/novel/article/poem/etc] I am submitting for possible publication [in/by] [name of publication or publisher].
I am a previously published freelance writer. My past writing credits include stories or articles in publications such as [list several publications related to current submission]. I also have experience in this area, as I am [list personal experience in area related to submission].
As always, thank you very much for your time and consideration. I look forward to hearing from you.