Adding terms and conditions allows you to require ticket buyers to agree to your organizations before they are able to purchase tickets.
Terms and conditions are added during the event creation process by clicking on Legal Policies & Important Info in the Advanced Settings menu
You will then need to click off the check box requiring ticket buyers to agree, and paste in the link for the external terms and conditions
Make sure to save the event and this will now show to the ticket buyer when they go to purchase a ticket!