\documentclass[12pt]{article}

\begin{document}
\section{Description of the used algorithm}
\subsection{Short theory}
\section{Functional description of the application}
\subsection{Input data format}
\subsection{Output text on console}
\subsection{Format of output data}
\section{Description of designed code structure}
\subsection{Own implementation tests}
\paragraph{Comments}
\subsection{Reference tests}
\paragraph{Source of reference values}
\paragraph{Comparision with our implementation}
\paragraph{Comments}
\section{Tests}
\end{document}