What exactly does contour function do?

Hello everyone! I am sorry to bother with a question that sounds so stupid but I am having a hard time understanding the contour function. What I want to do is given a grid on the x-y plane and a square matrix A, I want to plot the boundary of the e-pseudospectrum of A, that is for each point z on the grid, I compute the value s_min(I*z-A), that is the minimum singular value of the matrix I*z-A and I want to plot the points that satisfy s_min(I*z-A)=e. I was recommended to use the contour function, can anyone help me?