In the case that you want to globally turn off all notifications and ticket deliveries for all your events head over to Settings -> Order Settings and enable the feature "Never send notification email to customers when tickets are purchased or created with their email address."
Please note this will prevent all ticket deliveries and any kind of communication via email.
If you wish to control a specific event please go into the selected event - > "Event settings" and enable the feature "I'll manually trigger it, never automatically send tickets."
Evey will then wait for your approval before sending any tickets.