Is it compulsory to know all the basics of computers for taking admission to computer science engineering branch?

No, it is not compulsory to know all basics about computer for taking admission for computer Science engineering branch. If you don't know now, you can get admission in computer Science engineering and, then focus on your studies and improve your knowledge about computer.

Yes, it is mandatory for pursuing any engineering courses or any pro courses, such as medical engineering or commerce. Now a days, in any sector you should have a basic knowledge of CS.