Hello Sushil,
There are already many blogs which will explain this.
Searching in the this forum will help in getting all the details which are expecting.
However please check below ->
Uploading Files to SAP GW, Downloading Files from SAP GW - New Techniques
How To Upload and Download Files Using SAP NW Gateway SP06
File Upload/Download through NetWeaver Gateway
How to Read Photo from SAP system using SAP Gateway
Upload Image to SAP Gateway and Display Image in UI5 - Using New Fileuploader with SAP Gateway
Regards,
Ashwin