Grouping & Stacking
Each time you create a text box or a draw a shape, it is treated as a separate object. Grouping allows you to combine two or more objects into one single, movable, object. For example, a thought bubble can be made by drawing an oval and "stacking" a text box over it. To move the thought bubble around as a unit, "group" the text box and oval together.
The order (i.e., top-to-bottom) of a stack can be manipulated by going to Element > Arrange. Sometimes objects overlap each other and one of the objects "disappears," but even if some of the objects in a stack aren't "visible," their stacking order can be manipulated and they can be moved out of the group.