Go to the Keynote app 
on your Mac.
Open a shared presentation.
Click the slide in the slide navigator you want to begin with.
Click Play in the menu at the top of your screen and choose a playback option:
In Fullscreen: The slideshow plays on your primary display while the presenter display, with your notes and controls, is hidden. If you have a separate display connected to your Mac, the slideshow plays on your Mac while the presenter display is on the secondary display.
In Window: The slideshow plays in a window that you can share with your audience. To see the presenter display while the slideshow plays, move the pointer to the top of the slideshow, then click 
.
To start the multipresenter slideshow, choose Play > Play Multi-Presenter Slideshow (from the Play menu at the top of your screen). If another presenter has already started the slideshow, you can also click 
in the toolbar, then choose Play Multi-Presenter Slideshow.
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 
, then move the pointer over their name and click 
.
To stop sharing control with another presenter, move the pointer to the bottom of the screen to show the toolbar, click , then 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 , then turn off Show Presenter Notifications.