I have trouwble discretisizing the following Non-linear differential equation with stepsize h=\frac{1}{2}:

-y''+y^3=0 with y(0)=1, y'(1)=0

where y'(1)=0 is approximated with a second order differential formula.

I'm clueless, I don't quite understand what must be done here. Can someone offer me some guidelines?