EDI 810 Inbound AP invoice and 856 Inbound Receipts

Hi,
I wanted to know the following details.
1) I have to work on EDI 810 (AP Invoice Inbound)
    How can i get the mapping document for this like
    Which EDI field will be mapped to which oracle AP invoice interface column
2) I have to work on EDI 856 (ASN Receipt Inbound)
    How can i get the mapping document for this like
    Which EDI field will be mapped to which oracle Receipt interface column.
3) Is there any good note where i can get complete information on how to work
with EDI Gateways.

Please suggest.

Also i have mapped it to Utilities Community as i was not able to find the EDI community.