Hello Aspirant,


For admission into IITs for pursuing M.Sc courses, you will have to appear for IIT JAM examination.
IIT JAM stands for Indian Institute of Technology - Joint Admission Test for MSc, is a National level entrance exam which is conducted every year for students who wants to take admission in top institutes of India like IITs,NITs, CFTIs and IISC Bangalore.
And for PHD, various IITs organise a seperate called IIT PHD in which they offer admission to Ph.D courses.

i hope this helps.