How to create Function Module

Hi,

I am trying to create a function module using RSAX_BIW_GET_DATA_SIMPLE as a template. Can someone tell me how can I modify and rename this module. Also, how can I create extract structure from the function module.

I have tried to create a module in the module group by right cliking and then 'create', but it wouldn't let me do that way instead it giving me message 'function module name is reserved for SAP'. I get this message no matter what name I provide.

Basically I am trying to create a function module to extract data from SD module into BW. I appreciate your help with reward.

Thanks,

Rao.