How to create an hggroup for contour plot legend

Hello all, I need help creating a legend for a contour plot. I'm plotting a streamline function that is dependent of the x and y position. I have an x vector (1x15 vector) and a y vector (1x15 vector) and my streamline data at every point (15x15 array). I plot it all using contour(x,y,streamline_data), and it plots fine. However, I do not know how to use the legend to label the lines on the contour. I don't know how to use the hggroup input that needs to be specified for the legend. Please help!

-Colton.