From GroupScript documentation
HTTPS can be used for payment pages, where secure information is entered. To enable HTTPS you have to obtain SSL certificate from a vendor or your hosting provider. The certificate has to be installed on server- you should ask your hosting provider to help you with this.
After the certificate is installed, you should test it by entering https://yourdomain.com/ and see if you can open your page via HTTPS protocol. If the certificate is working (you might get a warning that part of page content is transferred via insecure communication- you can ignore that), you should enable HTTPS in Backend->Settings->Site settings->Use https.