If you need to make your customers agree to your terms and conditions on checkout, set $termsandconditions=TRUE; You will also need to create a page with your terms and conditions called termsandconditions.php & that will be shown in a 420 x 380 popup.
As it happens there is a new system now. Just make a content region called "termsandconditions" and that will automatically be used for the terms. Also, doing it that way will display the terms in a popup window such as the soft card, customer login and so on.