The videos below explain the process of uploading documents, creating document groups, assigning documents to capture forms, and creating a document request fulfillment action:
1) Uploading documents and creating a document group:
2) Assigning documents to a capture form:
https://help.leadliaison.com/watch/cTevrHniEXr
3) Adding the document group to an email and creating a document request fulfillment action: