While doing first post reviews, I sometimes find that the user didn't learn to use the toolbar just above the text field they write to. I didn't find any better help topic than those on editting and on Markdown/HTML formatting, but these tools are not explained there (doing the same by code might suffice for programmers on SO, but not for us). There is a similar question on meta.SO, but it focused on code formatting and the answers didn't link to any useful source.
What to do? I usually just say that there's such a toolbar, but I don't know a good source to link and whole manual is too long for a comment.