Hi,
You have to put the step "Term in condition" into your checkout workflow and you have to configure the "Terms and Condition" option (at the bottom left in the screenshot).
The "Terms and condition" option is a link to a Joomla article which would be displayed in the popup.
By adding the step into your checkout workflow, HikaShop would be able to know where it have to display the checkout "I agree..." with the popup link.
The "terms and condition" is about the order and not the registration.
If you want to put it for the registration, it is more a Joomla option but it could be done in HikaShop using some custom fields (but it might not have the same "clean" result).
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.