Click the Start as Host button in the multipresenter slideshow lobby.
The slideshow begins on the slide you selected.
As the host, you have control of the slideshow at all times, but you can also share control with other presenters. To share control with another presenter, move the pointer to the bottom of the screen to show the toolbar, click next to their name.
To stop playing the presentation, press Esc.
During a multipresenter slideshow, notifications alert you when a presenter joins and leaves the presentation, or starts and stops controlling the slideshow. If you do not want your audience to see the notifications, move the pointer to the bottom of the slideshow window to see the toolbar, click Add and view presenter notes in Keynote on Mac