You can use this page to play with the CodeDown WYSIWYG LaTeX editor, based on MathJax. It might help to look at the tips or choose from one of the examples.
If you like editing math this way, you can produce entire documents (and export them in PDF and other formats) by creating an account.
If you find bugs, please report them here, or come chat with us using Slack.
You can also type raw LaTeX in here and the editor will update.