There is documentation which the Sponsor is required to include in their section of the application; information about their income, their birth certificate, marriage registration or documents supporting common-law status.
The additional documents are outlined on the forms, in the Check List, and in the Supplementary Country guide where applicable.
Make sure you are reading all the instructions carefully. There is much more required than simply filling in the name and address
on the forms. Follow the Check List carefully, and check if there is a country specific Supplement for your country.