English translation of a German document, introducing the reader to the latest version—version 2ε—of LaTeX. This intro is widely recommended within the LaTeX community. (PDF).
LaTeX is the required format for many conferences in the technical fields, but even some conferences in the humanities and social sciences are starting to require it.
Many of the features of LaTex require that a software package be present in your compiler. Want to include math equations? Special fonts? Sheet music? Chemical structure diagrams? There's a package for each of those!