The drawing tool is useful for when you want to create a closed markup with specific dimensions.
Start by clicking the Drawing Tool on the right tool bar, and clicking your starting point on the map.
Type in the length you want the first segment to be, then press Tab and type in the angle you want the segment to be at from the starting point. Press Tab again to add a new segment and repeat inputting the length and angle. Once you have your desired drawing, press c to finish. If you do not do so yourself, finishing the drawing will automatically close the shape by connecting the last segment to the starting point.