\documentclass[10pt,a4paper]{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{amssymb}
\begin{document}
\section{Introduction}
TeXstudio is a cross-platform \LATeX ~editor.
Here you can see the spell-checking on different mispelled wrods: Tehy are autmaticaly underlind.
Mathmode: $\sum\limits^n_{i=1}\left(42*i^2\right)$
\section{More and more...}
\end{document}
