It's not clear if you are using app designer or guide. It should be simple enough to try. If you have trouble, share your code so we can help you.
As for the area, yes. Once you have finished drawing your polygon, use the polyshape and area functions. Here I've combined code from examples provided in the pages you and I have linked to.
I = imread('cameraman.tif');
roi = images.roi.Polygon(gca,'Position',[115 30; 80 45; 80 80; 115 90; 145 65]);
p = polyshape(roi.Position)