There are two parts in the main window : on the left side, there is the "potato" area where you can drop objects (eyebrows, noses, spectacles, ...) from the part on the right side, the "objects" area.
To drag an object, move the mouse pointer to the "objects" area, click on the object you want to drag, but do not release the mouse button until you have moved the mouse pointer to the location in the "potato" area where you want to drop the object.
Once dropped in the "potato" area, an object can be moved around in that area. Just click on it to select it for further drag and drop. When you click on it, it goes on top of other objects that were partially hiding it.
To remove an object that has been dropped in the "potato" area, drag it back from the "potato" area to the "objects" area.