Functional specification document in SAP for inbound interface

Dear experts,

Hope everyone is good!

I need to write a functional specification document on SAP SD inbound interface in EDI through idoc with few requirements. Can some one please assist me on how to start working on it and any inputs on that is much appreciated?

If there a sample document which I can refer to would be so grateful and it can be sent to <<Personal mail id removed>>

Thanks in advance!

Regards

Aaradhana