Beginning writers are always afraid of the cover letter. It can be a scary task. My advice is to keep it simple. Most editors don't hunker over cover letters with a magnifying glass determined to find fault - they don't have the time! Let your writing you submitted do the work. That said, cover letters are a necessary piece with almost all submissions. Always follow the publication's guidelines. My cover letters change all the time. This is just one variation.
#1 Basic contact information so the editor can reach you with a reply. Standard letter format, but make sure to include your email and telephone. #2 A specific contact name is always better than generic, however most of the time the publication does not list who to send your submission to and the masthead may have multiple names for each category. Some times I plop in "Fiction Editors" or "Poetry Editors". Personally, I think if the journal's uptight about this then they should list the name in their submission guidelines - what you should be following as you tweak your letter and document. #3 Get straight to the point. What are you sending them and why. If you have any connection to the publication, go ahead and state that here. Even if it's just that you enjoyed reading a specific story or poem in their journal. You almost never explain your story or poem, but in this case, I had a connection who suggested I submit to their themed issue. You should always follow through with opportunities. I thought my piece probably was not the tone they were looking for in that issue, so I added the explanation of how my story might fight within their theme. My last sentence in this first paragraph is almost always, "This is a simultaneous submission." This means you have sent that same story to other journals and the first one to accept it gets it. You must notify the other journals immediately that your story was accepted elsewhere. #4 In this paragraph list any relevant experience you have, whether it be other places you have been published or involvement in a writing community. If you have yet to be published, maybe list your education or life experiences for creative nonfiction. Keep it short and simple. #5 Always thank them for their time. If you have an author website, it doesn't hurt to direct them to it. Any publisher today, expects you to be building your own platform. #6 Not all journals request a bio, but it seems like more and more of them are saying to just include it in the cover letter. Bios can be another daunting task. Include any relevant writing information and then throw in an interesting personal fact or two. Watch the word count, sometimes it is listed in the guidelines. #7 Professional sign off. And, you are done! Better to not obsess over the details...just get it done and focus on the writing.