Go to Settings >> Checkout & Self-Serve Portal (under Customer-facing essentials) >> Legal Information and check Enable legal options. You will now see the fields to enter the agreement label and the corresponding hyperlinks to your legal terms and privacy policy pages. 

Furthermore, you have the option to display a checkbox to get the customer's consent for the agreement statement. Customers can check out only if they check this box. Here's a screenshot. 

If you're using the V3 checkout pages, here's how you can display the legal terms link on the checkout page.