The -4 is the starting point of the graph, in that he's plotted from -4
standard deviations to +4 standard deviations.  He's used a interval of 0.25
standard deviations between those points.  You can plot over whichever
range, and with whatever intervals, you like.

You have given the rather unhelpful fault description of "it didn't work".
If you want help, it may be worth telling us what results you got with which
formula and which input values, and what you expected instead.