Simple demonstration of TikZ

simple-arrows.tex

\documentclass{standalone}

\usepackage{tikz}
\usetikzlibrary{positioning}
\begin{document}
\begin{tikzpicture}[very thick,-stealth]
  \node (a) {A};
  \node [above right = 2em and 5em of a] (b) {B};
  \node [below right= 1em and 2em of a](d) {D};
  \node [right = 1em of d](c) {C};
  \draw (a) edge [bend left] (b);
  \draw (a) edge [bend right] (d);
  \draw (d) -- (c);
\end{tikzpicture}
\end{document}