Students need to apply for TIFR GS examination which is nationwide exam for MSc and PHd and similar PG courses. 

Based on cutoff scores of exam  candidates will be shortlisted for interview rounds and based in it final list of selected candidates shall be released for PG admission. 

After payment of fees admission will be grantes. 

http://univ.tifr.res.in/gs2019/Adm_Procedure/Adm_Procedure.htm