Writing mathematical expressions using Tex
The first thing you need to know about writing mathematical expressions is that you need to indicate where the mathematical expression begins and ends using markup tags. An easy way to do this is to hit the button in the editing toolbar that has a picture of a square root sign on it. The following is what you will see as a result of hitting this button:
<math>Insert formula here</math>
TeX is like a programming language that you use to specify the mathematical expression you want to have displayed. This specification gets compiled, and the image that appears on the website is the result.
(Note: MediaWiki doesn't support the full TeX language, instead MediaWiki "understands" a limited vocabulary of the TeX, LaTeX, and AMSLaTeX languages. Therefore, be aware that there are ways of doing things with these languages that may not work in MediaWiki.)
Here are some helpful links for writing mathematical expressions: