Open a MS Edge browser (you can't use Firefox. Something about the add-ons(?) will block you.). In the Edge browser (it could probably also be Chrome or some other browser) you log in to Overleaf.
My account using my yahoo mail, currently is free, which allows me only 1 other collaborator (or none). The next level is $155/yr, which is rather steep and probably means you'll need to plan on writing enough papers to make that worthwhile, per year. As a free account, it also means I will probably want to submit the paper separately from Overleaf. Overleaf, however, is very convenient in that it has a large number of templates for a wide range of journals, including those in Astronomy. You'll pick one and then start writing your paper and then just click the "recompile" button to see the code (on the left side of the Overleaf page) turned into final formatted text (seen on the right side of the Overleaf page).
For RNASS, you're permitted a maximum of 1500 words, including 250 max for the abstract. And that does not include the words for the Author Contributions section. That'll end up being ~3 pages of formatted text.
You are also allowed only 1 single Figure. However, that single figure can have many sub-figures (a), (b), etc, within it. In Photoshop, you can do that by starting with one of your figures, and then expanding the Canvas, and then use "file explorer" to drag/drop new images into your first image, then drag and resize them to tile it all together. However, in Photoshop I don't see a way to separately expand or contract the X and Y dimensions. So stretching only works for constant aspect ratio. If you need to make your image taller or fatter, you need to do that in Photoshop first while it's still a single image and then save that, and then drag that into your combined figure. There seems no rule on how how many sub-figures you can include. You should preserve detail as much as possible as TIFF images as you build your single image, and then as the last step, make the figure 300 dpi in resolution.
For our June 25, 2025 Quaoar occultation paper:
* It's relatively easy to submit through the AAS Journals author portal (https://aas.msubmit.net/cgi-bin/main.plex). You'll have to download the source code of the AAStex document. from your Overleaf page. You can download it using the "Menu" button on the top left, which should show you all the files associated with your project. Once you upload the source to the AAS portal, it automatically populates most of the submission form by parsing the Latex documents.
* Here's what the page of files for this project looks like. Note that you have to tell it what kind of document it is. "manuscript" should be the "main.tex" code from Overleaf. Inside Overleaf you can click on the top arrow and generate the "author-generated PDF" which is also to be submitted on the AAS site. By having a separate "main.tex" file and figure file, with the other files, you should get a "system-generated" PDF file which looks right. If not, and if you are sure you've uploaded all the files, you can explain at the end in your cover letter which files are which and that their system did not generate the PDF automatically.
* for keywords, go to the UAT and search for the reference number for their formal list of key words for Astronomy.
* If you click in the AAS submission page on the submit link on RNAAS, there will be several "pages" of web forms to fill in. Amongst those will be author addresses/details, an upload page for files, and a cover letter section.
* The cover letter (from memory) will either have to be attached, or you can fill in the available box. This is where you should put *any* extra thing you want to mention to the editor. (Near the end of the process don't trust that they did any of it, you'll want to check and then tell them if they didn't do it and to fix it before publication.)
* The file upload section will tell you what files you need. Typically you would include a complete pdf and all the Latex and image files so that the page can compile its own version of the pdf. Hopefully all the files you need can be got by a simple download of the source from Overleaf.
* Key words, since 2019 are from the UAT. Search here . If nothing comes up, then it's just not in the UAT, it doesn't seem to think too hard about related concepts. So, just keep trying and it may eventually find something and give you the (###) reference number in parens too, which AAS seems to want in their keyword list. For example "Planetary satellites (1089)" and
* Sometimes it requires some sort of built file to do with the bibliography (output.bbl). That's a bit more complex. There are instructions you can find via web search on how to do that. But not every journal requires that... In brief, there is a button next to the compile button that has the full expanded log, and an option down the bottom of that page which you can expand to show all the log files, you have to do that and then click on the log file you want to d/l it.
For arXiv...
ArXiv have published criteria for short publications (https://blog.arxiv.org/2019/06/21/policy-on-short-works/)