\documentclass{standalone}
\usepackage{mathtools}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
\draw [thin,->] (-3,0)--(3,0) node[below]{$x$};
\draw [thin,->] (0,-1.1)--(0,1.3) node[left]{$\operatorname{erf}(x)$};


\draw [thin,dotted] (-3,1)--(3,1) ;
\draw [thin,dotted] (-3,-1)--(3,-1) ;



\draw[red] plot[domain=-3:3,smooth] function {erf(x)};

\draw[green] plot[domain=-3:3,smooth] function {erf(x/2)};

\draw[magenta] plot[domain=-3:3,smooth ] function {erf(2*x)};

\draw[blue] plot[domain=-3:3,smooth ] function {erf(3*x)};





\end{tikzpicture}
\end{document}