\documentclass[10pt,a4paper,twoside]{article}
\usepackage[utf8]{inputenc}
\begin{document}
\section{Placek}
Co \textbf{z} oczu,\\\textit{t}o \textsl{z }serca.
\begin{center}
Ciemnota -- gorsza od zbrodni.
\end{center}
\section{Placek2}
nyetge

\end{document}