Free & Interactive Online Introduction to LaTeX by John Lees-Miller.

From the webpage:

Part 1: The BasicsWelcome to the first part of our free online course to help you learn LaTeX. If you have never used LaTeX before, or if it has been a while and you would like a refresher, this is the place to start. This course will get you writing LaTeX right away with interactive exercises that can be completed online, so you don’t have to download and install LaTeX on your own computer.

In this part of the course, we’ll take you through the basics of how LaTeX works, explain how to get started, and go through lots of examples. Core LaTeX concepts, such as commands, environments, and packages, are introduced as they arise. In particular, we’ll cover:

- Setting up a LaTeX Document
- Typesetting Text
- Handling LaTeX Errors
- Typesetting Equations
- Using LaTeX Packages
In part two and part three, we’ll build up to writing beautiful structured documents with figures, tables and automatic bibliographies, and then show you how to apply the same skills to make professional presentations with beamer and advanced drawings with TikZ. Let’s get started!

Since I mentioned fonts earlier today, Learning a Manifold of Fonts, it seems only fair to post about the only typesetting language that can take full advantage of any font you care to use.

TeX was released in 1978 and it has yet to be equaled by any non-TeX/LaTeX system.

It’s almost forty (40) years old, widely used and still *sui generis*.