Hi Ranendra,
Since you are practicing in Sand box itself you can get your self SAP_ALL and SAP _ NEW profiles which would help you to explore each and every thing which you want to create and there would be no issues for authorization.
Also Since you are using Flat File as Source systems Please make sure you go to
RSA1-> Source systems -> File-> Right Click--> Check connection. If it appears ok please go ahead with your activities and if you get any issues related to connection please approach your Basis team.
Please revert in case you need any further details.
Thanks & Regards,
RDS