I want , about knowledge what should do after graduation in B.Sc.

Hi, to stand a much better chance of getting a well-paying job, I advise you to complete a Master of Science (M.Sc) degree provided by a recognized university.
Otherwise, you can also do an M.B.A. for career diversity and expansion. This is also useful if you wish to do a corporate job in future.
If you wish, you can try for jobs instantly after graduation. Many government sectors like UPSC, nationalized banks, railways etc. require B.Sc. graduates on a constant basis. You can try for these and private company jobs through job portals, newspapers, and known contacts.