Configuration of source schema depends on the type of data you are receiving from partner.
If receiving EDI Data from Partner
The source schema (EDI schema) defines the layout of EDI message and you can use it to parse the inbound EDI message as per EDI Message Standards. For details, refer to Creating EDI Schema section.
If receiving Non EDI Data from Partner
In case of non-EDI data, you need to create the schema based on the format of inbound data. For example, if the incoming data is an excel file, you have to create an Excel schema.