Hi,
maybe you already know these document:
IDoc Basics For Functional Consultants
or even check the attachments of this OSS Note too (for SAP Business One):
1580236 - MX – Electronic Documents (CFDI Model)
here you will find this document:
How_to_Implement_and_Use_Electronic_Documents_with_SAP_Business_One_8_81_PL08.pdf
Best regards,
Pablo