You need to find identical 3D objects on the ground and place them on the platform! It seems easy, but with each level the game becomes more difficult - and it becomes increasingly difficult to find two identical objects in a pile of other three-dimensional objects.
Computer: Hover the cursor over the object and, holding down the left mouse button, move it to the platform. Collect all paired items. Mobile devices: Select an item and move your finger across the screen to move it onto the platform. Collect all paired items.