The American Astronomical Society (AAS) has developed a markup package to assist authors in preparing manuscripts intended for submission to all the AAS-affiliated journals. The journals are the Astrophysical Journal (ApJ), the Astronomical Journal (AJ), ApJ Supplements (ApJS), Letters (ApJL), The Planetary Science Journal (PSJ), and Research Notes of the American Astronomical society (RNAAS). The latest LaTeX classfile is AASTeX v6.3.1 and it can be obtained here. The sample631.tex template uses this classfile to illustrate some of the newer features for submissions to the main Journals. Authors should consult the extensive guide for all the features in AASTeX v6.3.1. Once your manuscript is complete, simply use the "Submit to Journal" option in the Overleaf editor to submit your files directly to the journal for processing. Note that you will still need to log on to the submission site to supply additional meta-data. The editorial office will contact you when your submission has been processed and is ready for further input. If you're new to LaTeX, check out our free online introduction to help you get started, or please get in touch if you have any questions.