At this point you should not be concerned about Source Document Framework, but only about the document storage, UI and perhaps some domain logic responsible for processing the document. Storage usually consists of two tables, one for storing document header information (MyDocumentHeader) and another one to store document lines information (MyDocumentLine). The UI usually requires creating a list page and a document entry form. The List page and the form would be using the domain logic tables and classes that implement whatever functionality is required for the document.
The subsequent steps will be outlining how to employ Source Document Framework for your newly created document.
For additional examples and detailed code samples refer to existing source document extensions in Dynamics AX 2012.
A good example of a less complex document is Free Text Invoice. Good examples of complex documents are Vendor Invoice and Purchase Order.
Refer to classes and tables related to SourceDocument_CustomerInvoice and SourceDocumentLine_CustomerInvoice enums for Free Text Invoice source document extension code.
Refer to classes and tables related to SourceDocument_VendorInvoice and SourceDocumentLine_VendorInvoice enums for Vendor Invoice source document extension code.
Refer to classes and tables related to SourceDocument_ProductOrder and SourceDocumentLine_ProductOrder enums for Purchase Order source document extension code.