This is done by using the some process steps:
These steps are given below. and go through that steps.

1. Analyze the data from the local file or flat file.
2. Analyze the transaction.
3. Declaring the internal table (BDCDATA)
   program: name of the module pool program name
   dynpro: screen number.
   dynbegin: it indicates for the new screen.
   fname: name of the fields in  the screen
  fval : the values are assigned with the fields.
4.Transferring the data from the local file to internal table
5. Populating the internal table.

USe IDOC_INPUT_ORDERS as mapping.  The standard IDOC uses 
BDC for posting, details will be found in the function 
module.