MathJax is an open source JavaScript engine for mathematics in web browsers. We use the TeX-AMS-MML_CHTML configuration, which allows math to be specified in TeX, LaTeX, or MathML notation, with the AMSmath and AMSsymbols packages included. The CommonHTML output processor is used by default, which has the best performance on modern browsers. You can employ the MathJax contextual menu to select other renderers as you like.

To use the shorthands \(...\) and \[...\] as delimiters for mathematics in LaTeX, you should esacpe the backslash as \\. So, it is better to use $...$ and $$...$$ or the corresponding environments defined by \begin{}...\end{} instead. Please have a look at the MathJax demos to get some practical examples. We also have some tips for typesetting math in LaTeX using MathJax:

• Don't use too many small spaces like \; and \: for fine tuning. In most cases, they are abused.
• Don't waste space if two short expressions can be put on the same line. You should use \quad to seperate them.
• Don’t use \frac in-line. Use that only if you are setting aside the equation.
• To get a dollar sign in text, you can use \\$ or something like <span>\$</span> to isolate it.
• You can use \slashed to produce the Feynman slashed-character notation.
• Always put spaces around symbols for better readability and try your best to arrange math in a presentable way.

If you are looking for an online LaTeX formula editor with live preview, HostMath, JaxEdit, and ShareLaTeX are good choices. If you would like to try out MathML, RyPress’s tutorial and Daniel I. Scully's guide both provide a gentle introduction.