hi,

if you have already completed masters course in mathematics, you may apply for phd courses on iits iiscs, indian statistical institute. gate score holders are eligible for applying in different research organization like isro, drdo etc for scientist position. also there is some programs in iits which takes only mathematics background students who are having gate score is :

IIT Bomaby IEOR

IIT Madras Industrial Mathematics and Scientific Computing

IIT Kharagpur Computer Science and data processing

you may apply as junior research fellow position in different state universities or nits or iits when vacancy comes using your gate score.