First, create an unlinked page named "Terms and Conditions"
Next, add a checkbox field to your form that only has one option "I Agree" and make it a required field. Put the following code in the field name:
I have read, understand, and agree to the website <a href="https://www.yoursite.com/terms-and-conditions" target="_blank">Terms and Conditions</a>.
I've included a screenshot of how I did something similar on one of my clients' sites.