Flat file to Iinbound DOC conversion

I have requirement to pick up file up the .txt input files from INPUT archive folder of Seeburger system, converting them to IDOC to trigger the SAP XI system.

I am developing pOC on it.

Idoc is inbound.It use program for creating idoc RSEINB00.

Can any one tell me stepwise procedure to create Idoc?

Please focus more on we21 transaction that which parameter we can put in it?

I wanted to pick up file from my local system.Is it possible?