As a facilitator, you will see the list of speakers. Open Slides will take the order of stack automatically. To take a person’s stack, click the play icon. This will bump the comrade to the current speaker. Once you take stack the persons line will light up a different color like the image below.
To end a person’s stack, click the square or stop icons. This will remove them from the stack and let you know who the next person is in the stack.