After the selection of the country, product category, product, you get a list of possible certificate templates. Once you have selected the appropriate template you get the description of the product details and the certificate annex types.
After completing the certificate (xml) and all its related data, when posting the data through the API, the request will be validated following the business rules associated with the certificate status (Draft, Initiated, Completed). The treatment of your requested certificate will be started at the status Completed see here for more info.
CertificateRequest and ProductDetail can be constructed and downloaded in XML.
See an example here.