To switch the 'Terms & Conditions' on/off, from the store dashboard go to:
> Store Settings > Checkout > Terms

From within this page, the top tick-box labelled 'Show at checkout' will either enable or disable the feature. The 'T&Cs text' and 'Error text' boxes underneath can be customised to your liking.
(*Don't forget to click 'Save Changes' after making alterations*)