How can I plot $f(x, y) = x^2 + y^2$ I want to plot $f(x, y) = x^2 + y^2$?
I can plot functions of a single variable but I don't know how to plot multivariable function.

The graph of this function will be a surface in space. Above the point $(x,y)$ in the plane it has height $f(x,y)$.

https://www.mathcurve.com/surfaces.gb/paraboloidrevolution/paraboloidrevolution.shtml
