If someone already worked with EDI and ASN, please explain me what is the functional group header and how can I get one.

or maybe.. just give me a site where I can get all the information to know how to do a Advanced ship Notice, how it works.

All the information I have now, is the information to know what is the signification of ISA, GS, BSN.. etc.. But I don't know how to "code" it.

Thank you.
If someone just have little information, please tell me.

Roxane