Randomizing Drag and Drop Items - HELP!!! (I'm new to Storyline 360)

Those different levels on the timeline represent the Z-coordinate of the objects. The ones that are higher in the list cover the ones that are lower.

If you have made this as a Freeform Drag and Drop, you can go into the Form View, and asssign each to a target. Each object can have only one target, but targets can have multiple objects. Once they are assigned, “Reveal one at a time”, and “Shuffle” will work.