Anybody who has to typeset mathematics will know that conventional word processors make a pretty bad job of things. The reason is that there is a 'grammar' for typesetting formulae and getting good results requires more than just laying out the symbols in the right order.
Donald Knuth wrote a typesetting system that was intended to produce machine portable output of quality comparable to the best human-typeset documents. The system is not terribly comfortable for people from the modern what-you-see-is-what-you-get tradition, but the results are superb, and as a result Knuth's TeX system and its derivatives are the standard for technical academic publishing.
LaTeX (Lamport's TeX) is macro package layered on top of Knuth's 'plain' TeX. In pratice, most people use LaTeX now. Some years ago I wrote a short book on using LaTeX which some people find useful. There are now later versions of LaTeX which you can read about elsewhere, but by all means try this (now free) book if you like. Please only make a personal copy for yourself: do not breach my copyright by distributing this document.