Here are the Code examples of this chapter. You can compile them online right on this web page by pressing the Typeset / Compile button. You can also edit them for testing, and compile again.
For a better view with the online compiler, I sometimes use \documentclass[border=10pt]{standalone} instead of \documentclass{article}. Instead of having a big letter/A4 page, the standalone class crops the paper to see just the visible text without an empty rest of a page.
Any question about a code example? Post it on LaTeX.org, I will answer. As forum admin I read every single question there. (profile link).
Error testing
\documentclass{article}
\begin{document}
% wrong:
%\Latex\ says: Hello world!
% correct:
\LaTeX\ says: Hello world!
\end{document}
Warning
\documentclass{article}
\renewcommand{\familydefault}{\sfdefault}
\begin{document}
\emph{Hello world!}
\end{document}
This code is available on Github. It is licensed under the MIT License, a short and simple permissive license with conditions only requiring preservation of copyright and license notices.