Remember that function notation is like slope-intercept form, but you replace y with f(x).
The y-coordinate is -4.
Therefore, f(x) = -4
Why is there no x? Well, the slope is 0, so the x is unnecessary.
[tex]\bf (\stackrel{x_1}{-3}~,~\stackrel{y_1}{-4})~\hspace{10em} slope = m\implies 0 \\\\\\ \begin{array}{|c|ll} \cline{1-1} \textit{point-slope form}\\ \cline{1-1} \\ y-y_1=m(x-x_1) \\\\ \cline{1-1} \end{array}\implies y-(-4)=0[x-(-3)] \\\\\\ y+4=0(x+3)\implies y+4=0\implies \stackrel{y}{f(x)}=-4[/tex]
