\begin{document} \begin{tikzpicture}[domain=0:4] 
\draw[very thin,color=gray] (-0.1,-1.1) grid (3.9,3.9); 
\draw[->] (-0.2,0) -- (4.2,0) node[right] {$x$}; 
\draw[->] (0,-1.2) -- (0,4.2) node[above] {$f(x)$}; \draw[color=red] plot (\x,\x) node[right] {$f(x) =x$}; \draw[color=blue] plot (\x,{sin(\x r)}) node[right] {$f(x) = \sin x$}; 
\draw[color=orange] plot (\x,{0.05*exp(\x)}) node[right] {$f(x) = \frac{1}{20} \mathrm e^x$};
\end{tikzpicture} \end{document}