Well the baggy clothes makes it hard to see a shape, but you appear to be a straight up and down as your hips appear to be the same width as your shoulders, however with your arms held in the position they are in that is also hard to tell. If that is your true shape then i would suggest a dress that pulls you in at the waist. However i could be completely wrong due to reason i have already pointed out
Try this - put in your measurements and Dressipi will 1 - say something nice about your shape 2 - tell you what sorts of styles you should wear 3 - tell you what styles you should avoid 4 - link you to actual clothes available in the shops that fit what it said in #2
Is there a diagram? I think you measure around the largest part, because they are trying to see what size clothes you will fit into. They have all of the size charts for all of the shops in a spreadsheet or something so they can tell you that you'll need a size 14 in Zara but a 12 in. Dorothy Perkins, for example.