BDC PROGRAM IN ABAP

1. A BDC program is used for all of the following except:

A: Downloading data to a local file

B: Data interfaces between SAP and external systems

C: Initial data transfer

D: Entering a large amount of data

I want to learn how to upload data using BDC. If I have a excel data file how will upload it using BDC. I don't know the full process of doing it, if someone help me in this. I want it using BDC session process and processing that session. I was trying to upload material master other day. But could not follow the process of uploading using BDC though I know LSMW.

Confused? Feel free to ask

Your feedback is always appreciated.I will try to reply Ur queries as soon as time allows.
Regards,
SAPhelpdesk