basics about surface plot

Hi, I'm trying to do the "2d advection equation" and I'm stuck with the way you need to plot surface. I apologize in advance for possible unclear things in my question because I don't really know how to put it in words.

So this is the equation : 1d advection in 2D we just need to derivate it for dy too

But even before that.

Mathematically you start with C0=[C(x) ; C(y)]. (In my case C(x) and C(y) are vector made with a gauss equation thus making C0 a matrix 2xN)

I've understood that the first step is to create a grid with meshgrid in order to tell the program the range of x and y axis.

Then I don't know. The idea is to represent to concentration like that. So far my code looks like this:

clear, clc, clf
#Gauss curve equation
dx=0.1; #step size x
dy=0.5; #step size y
Lx=-5:0.1:5; #range of domain x
Ly=-5:0.1:5; #range of domain y
dt=dx.^2/2.5; #time step size
Gx=exp(-Lx.^2); #initial concentration x based on gauss curve
Gy=exp(-Ly.^2); #initial concentration y based on gauss curve

#variable
V1=1; #velocity1
V2=2; #velocity2

#Advection in 2D
Cx=Gx;
Cy=Gy;
C=[Cx ; Cy];
[X Y]=meshgrid(Lx,Ly);
contour(X,Y,C)

I read the different information about function like contour, mesh, griddata but they are a bit rough for me and they don't help me to understand how matlab thinks .

Thank you in advance for your help.