Turning Off Notifications While Presenting
Simplest way is Option (⌥) + Click Notification Centre button; top right corner. It should make the NC dim.  ⟶ 
Open NC then go to Today tab scroll up, it should show Do Not Disturb button, just turn it on.

@Buscar웃 said you can also turn on the keyboard shortcut in System Prefs -&gt; Keyboard -&gt; Shortcuts.