What is a workplane in TinkerCAD?
Think of the workplane like the floor. If I was going to build a chair, I cannot just build it in mid air, I need to put my tools, wood and other things on the floor. The workplane is the big blue highlighted object.
When you drag out an object it is dragged out and sits on the same level as the workplane. Its like putting a chair on the ground, it does not float right?
The cool thing about the workplane is that you dont need to put all the object ON the workplane. Look at the other objects, they simply are sitting on the same level as the workplane.