LaTeX is a typesetting program designed to produce high quality layout with minimal input from the document author. The concept is to separate content from design. You create a text document with a few tags indicating certain content (author, chapter titles, tables, etc). You run your text document through a LaTeX program, and you produce a graphical file (I use pdflatex to produce pdf files) of your content.
This frees you to focus on content when creating a document, and lets the computer worry about page breaks, justification, hyphenation, indentation, etc.
It sounds more complicated than simply using a word-processing program, and perhaps in some ways it is. And though you get higher quality results, it’s definitely not for everyone.
Learn more about it: