This question already has an answer here:
When asking questions on Math.SE, the "MathJax help »" link on the sidebar points to MathJax basic tutorial and quick reference, which in my opinion is very friendly to users who have never heard about MathJax before.
However, on many other sites, the help link points to something like a complete documentation, which seems to be too complete for new users.
Due to its brevity and helpfulness, I think we should use MathJax basic tutorial and quick reference as a crash course on all SE sites, maybe after immigrating this post to Meta Stack Exchange if necessary.
Actually, I've found this similar question, but after nearly 2 years, it received 0 answers and even 0 comments. Also, that post consider this problem a "bug", but I think it should be a "feature request". This is why I'm posting my own question now.