Hi Shashank,
You may create a custom function module which is RFC enabled . The contents of function module should be based on your requirement to select data from respective tables and export the content to a parameter tables which will be transferred to calling application ( .NET in your case).
Within .NET application you may define belowSAP connection parameters to establish the connection :
SAP gteway host
SAP instance
SAP client
User and password
You may call above SAP functional module from your .NET application to pull required data,
Hope this helps.
Regards,
Deepak Kori