This figure shows an empty slot with the name of a selected asset being dragged over it. When the slot is surrounded by a green border (as shown in this figure), it means the slot accepts that type of content and that you can drop the asset into the slot.
Click the name of the asset you wish to place in the slot and hold down the button on the mouse to drag it.
Drag the asset's name over the slot.
When the slot is surrounded by a green border, drop the asset into the slot.