Your first LaTeX document
The parts every document has: the class, the preamble, the body, sections — and how to compile.
The three parts
Every LaTeX file starts with \documentclass, which chooses the layout (article, report, book, or a journal class). Between it and \begin{document} is the preamble, where you load packages and set the title. Everything you want printed goes between \begin{document} and \end{document}.
\documentclass{article} % the layout
\usepackage{amsmath} % preamble: packages and settings
\title{My first document}
\author{Your Name}
\begin{document}
\maketitle
Hello, world!
\end{document}Sections and paragraphs
Use \section, \subsection and \subsubsection for headings; they are numbered automatically. A blank line starts a new paragraph — single line breaks in the source are ignored, so you can write one sentence per line.
\section{Introduction}
This is the first paragraph.
This sentence is still in the same paragraph.
This one starts a new paragraph.
\subsection{Background}
\subsubsection*{An unnumbered heading}Compiling
Press Compile (or Ctrl+Enter) to build the PDF. If something is wrong, the log explains it in plain words and often has a one-click fix. Lines starting with % are comments and do not appear in the PDF.