The engine running Jmol Wiki is called MediaWiki.
There is no help section included here, but you can visit these external links that explain how to edit pages in any MediaWiki-based wiki (including Wikipedia).
Quick help or reminder:
Includes links to cheatsheets designed to be printed: MediaWiki reference card and poster-size cheatsheet, available in many languages.
More detailed help:
Help Editing, from Meta-Wiki (MediaWiki Handbook)
How to edit a page, from Wikipedia