Sketch graphs by hand and use them to make approximations for each of the limits. If a two-sided limit does not exist, describe the one-sided limits.
$$
\lim _{x \rightarrow 0} f(x), \text { for } f(x)=\left\{\begin{array}{l}
2 x+1, \text { if } x \leq 0 \\
2 x-1, \text { if } x>0
\end{array}\right.
$$