"Don Knuth's Tau Epsilon Chi (TeX) is potentially the most significant invention in typesetting in this century. It introduces a standard language in computer typography, and in terms of importance, could rank near the introduction of the Gutenberg press."
--Gordon Bell, forward to Tex and metafont, New Directions in Typesetting
What are TeX and LaTeX? Kevin O'Malley writes in LaTeX: It's Not Just for Academia, Part 1
LaTeX is composed of two main systems: TeX and a macro package that sits on top of it called LaTeX. In this article, I will use LaTeX to refer to the entire system.
TeX (pronounced Tech) was written by Donald Knuth in the late 1970s. If you are not familiar with Donald Knuth's work, stop now and check out his web site. Knuth is considered one of the pioneers of computer science and his books have influenced generations of programmers and computer scientists. TeX came to life because of Knuth's frustration with the quality of typesetting for his books.
As Knuth writes in the foreword of The TeX book, "TeX is a new typesetting system intended for the creation of beautiful books--and especially for books that contain a lot of mathematics. By preparing a manuscript in TeX format, you will be telling a computer exactly how the manuscript is to be transformed into pages whose typographic quality is comparable to that of the world's finest printers."
The TeX software is basically a macro processor, with an accompanying macro package called Plain TeX. TeX is exceedingly stable. In fact, Donald Knuth offers a reward if you're the first person to report a new error.
LaTeX (pronounced Lah-tech) is a macro package written by Leslie Lamport. This macro package uses the typesetting functionality of TeX, but adds high-level abstractions that simplify the creation of documents. According to the TeX FAQ, "LaTeX allows markup to describe the structure of a document, so that the user need not think about presentation. By using document classes and add-on packages, the same document can be produced in a variety of different layouts."
To sum up, TeX provides typesetting facilities, and LaTeX provides the high-level macros that make TeX easier to use, and it simplifies the creation and production of documents.
To use LaTeX, you first compose a LaTeX source file. A LaTeX source file is a text file with a .tex extension, which consists of your writing content and LaTeX control sequences. Next, you pass the document to the LaTeX system, where it reads the document, processes the file, or files, and produces its output files. In practice, the process is more complex.
The primary strength of LaTeX is its typesetting quality. It effectively enforces a consistent and professional layout and typographical convention for your document. As such, it provides structure to your document and makes it far more professional and readable. Additionally, it relieves you from thinking about the visual aspects (form) of the document and making ad hoc decisions concerning the document's appearance. This enables you to think about the substance of your writing and let LaTeX worry about the form of the document, and it allows you to produce the highest quality output.
Another nice feature of LaTeX is that it renders your source document in many output formats. For example, imagine writing your resume in LaTeX and producing a PDF, Postscript, HTML, and RTF version--all from a single source file and rendered in the highest quality output.
LaTeX is a document preparation system ideally suited for writing technical papers, books, and other documentation. Many journals accept LaTeX files at the final submission stage, greatly reducing the number of typographical errors that might otherwise appear in published works.
A number of freely-available versions of LaTeX exist for various platforms. If you are using LINUX, you probably already have LaTeX on your system. Otherwise, look here to find a distribution for your system.
CTAN, the Comprehensive TeX Archive Network, has many links to useful documentation, programs, TeX and LaTeX distributions, etc.
Some useful documentation written by others:
The short guide by Oetiker et al. is a good place to start.
BibTeX is a tool and file format used to describe and process lists of references in conjunction with LaTeX. This offers several advantages:
LaTeX versus WYSIWYG word processors:
An easy way to learn LaTeX is by example. Here is the LaTeX file that I used to produce one of my recent papers; here is the PDF file with the paper. Note that in line 35 of the LaTeX file, I load a style file, pww.sty, that contains a number of commands or macros that I have defined. In addition, I used BibTeX to handle citations. Click here to see an example of a BibTeX database.