how would i go about graphing
f(x,y,z)= -1
or any constant for that matter...?
you can't.
for functions of the form w = f(x,y,z) it takes three dimensions for the domain and would require a 4th dimension for the range which humans can't do.
One way of thinking of this is think of f(x,y,z) as the temperature at any point in 3 space. In your case the temp is -1 everywhere.
You can't visualuze temperature in your 3 -D world can you human?
Actually you can if you add color as with infrared imaging
if for example f(x,y,z) = x^2 + y^2 +z^2
then f(x,y,z) = 1 woulde be the level surface
x^2 + y^2 +z^2 = 1
meaning that on a sphere of radius 1 f has the same value at all points.
This is analagous to the level curve for fns of 2 variables