Here is a simple example, which I hope you can bend to your needs. I adapted it from the documentation here: http://www.mathworks.com/help/techdoc/ref/contour.html. I think it illustrates most of what you want, including how to overlay multiple plots (with the hold command), adding labels to the contours, etc. There are help files for all the different functions I used, of course.
figure
hold on
[X,Y] = meshgrid(-2:.2:2,-2:.2:3);
Z = X.*exp(-X.^2-Y.^2);
[C,h] = contour(X,Y,Z);
set(h,'ShowText','on','TextStep',get(h,'LevelStep')*2)
addedRandomX = rand(1,20);
addedRandomY = rand(1,20);
plot(addedRandomX, 1+addedRandomY,'kx')
plot(-addedRandomX,1+addedRandomY,'ro')
