To get your diagram to look exactly as you want, you may need to reorder your shapes. One way to do the reordering is via the canvas layers. This will become very tedious if you have a big diagram, also best practises regarding canvas layers are to stick conceptually equal shapes on the same layer.
This section will teach you to reorder shapes within the same layer.
Start with three shapes drawn in the following sequence: Square, Circle, and Cloud. Let the Circle overlap the Square and let the Cloud partly cover both the Square and the Circle. Inside the square, write 1, inside the Circle write 2, and inside the Cloud write 3. These numbers indicate in which sequence the shapes where created.
What you have done here is for each new shape you draw, the shape will be put on top of the other shapes. If you never draw overlapping shapes, you may not have noticed this at all.
If you try to drag the circle in and out of the group of shapes, it will still be sandwiched between the...