Lesson 3

# LaTeX document structure

This lesson shows the basic structure of a LaTeX document, and how to build it into a PDF file, as well as the main special characters used to control LaTeX.

Your first LaTeX document is going to be very simple: the idea is to show you how a document looks and how to typeset it successfully. It is also your first chance to see how to use the examples here on learnlatex.org.

If you are using a local LaTeX installation, in your editor create a new file called first.tex, and either copy–paste the text below or type it in.

If you are using the online system, you can just click on the ‘Run at TeXLive.net’ or ‘Open in Overleaf’ buttons in the example to try it out!

We suggest you try out the online options even if you have set up LaTeX locally; this is a good chance to see how the different options work.

\documentclass{article}
\usepackage[T1]{fontenc}

\begin{document}
Hey world!

This is a first document.
\end{document}


Save the file and typeset it to a PDF document; if you are using a local LaTeX installation, the exact button to press will depend on the editor you have picked. You should get a PDF file that contains the text above plus a page number; LaTeX adds that automatically.

View the output first.pdf with whatever program you prefer for PDF viewing. Looks great; congratulations!

If you want to get HTML rather than PDF output, take a look at the help for how you can do that.

## Handling errors

Errors happen. Check that you have entered each line in the text file exactly as written above. Sometimes seemingly small input changes give large changes in the result, including causing a document to not work. If you are stuck, try erasing the document and copying it fresh from the lines above.

If your LaTeX typesetting run ends with a question mark then you can get out by typing x and <Enter>.

LaTeX’s error messages try to be helpful, but they are not the same as messages in word processors. Some editors also make it hard to see the ‘full’ text of an error, which can hide key details. LaTeX always creates a log of what it is doing; this is a text file ending in .log. You can always see the full error messages there, and if you have a problem, expert LaTeX users will often ask for a copy of your log file.

We cover more about dealing with errors in lesson 15.

## What you’ve got

The first document shows the basics. LaTeX documents are a mixture of text and commands. The commands start with a backslash and sometimes have arguments in curly braces (or sometimes optional arguments in square brackets). Then you get an output PDF by telling LaTeX to typeset your file.

Every LaTeX document has a \begin{document} and a matching \end{document}. Between these two is the document body, where your content goes. Here the body has two paragraphs (in LaTeX you separate paragraphs with one or more blank lines). Before \begin{document} is the document preamble, which has code to set up the document layout. The \usepackage command is described in a later lesson it is used in most examples on this site to set up the font encoding.

LaTeX has other \begin{...} and \end{...} pairs; these are called environments. You must match them so that for every \begin{x} there has to be an \end{x}. If you nest them, then you must have \end{y} ... \end{x} to match \begin{x} ... \begin{y}, i.e. the \begin and \end statements matching in order.

We can add comments to a LaTeX file by starting them with %; let’s use that to show the structure:

\documentclass[a4paper,12pt]{article} % The document class with options
\usepackage[T1]{fontenc}
% A comment in the preamble
\begin{document}
% This is a comment
This is   a simple
document\footnote{with a footnote}.

This is a new paragraph.
\end{document}


You can see above that we’ve got two paragraphs: notice the use of a blank line to do that. Also notice that multiple spaces are treated as a single space.

You might also sometimes want a ‘hard’ space that does not break over lines: in LaTeX we can create that using ~, ‘tying’ two pieces of text together. That’s particularly useful when we start creating cross-references later in the course.

## Special characters

You’ve probably spotted that \, { and } have a special meaning to LaTeX. A \ starts an instruction to LaTeX: a ‘command’. The curly brace characters { and } are used to show mandatory arguments: information that commands require.

There are some other characters with special meaning; we’ve just seen that ~ is a ‘hard’ space, for example. Almost all of these characters are very uncommon in normal text, which is why they were chosen for special meanings. If you do need to show one of these special characters, we’ve put some information in the further details page.

## Exercise

Experiment with the online editing and typesetting system; click the button to typeset the content, then edit it in the webpage and re-typeset it.

Try adding text to your first document, typesetting and seeing the changes in your PDF. Make some different paragraphs and add variable spaces. Explore how your editor works; click on your source and find how to go to the same line in your PDF. Try adding some hard spaces and see how they influence line-breaking.