To play with the Slot, click on the symbol indicated by the red arrow in the next image.

Then click on the green button at the lower center of the slot to enable it (see the yellow arrow in the following image).

Or you can click on the green AUTO button and the slot will play by itself until you click it again (indicated by the yellow arrow in the image below)

When you want to close the Slot, click on the red X icon (green arrow).