To join M.Tech, you have to qualify GATE and apply through the websites of COAP for IITs and CCMT for NITs and some other collges (The list of participating institutes is given in their website - https://ccmt.nic.in/webinfo/Public/Home.aspx). If you are asking about JNUTH, you can apply to it with your GATE score. The official notification regarding that will be mostly released after the TS PGCET 2018 is over. So, you've to wait till that. Be in touch with the websites of JNTUH and TS PGCET, so that you won't miss anything.

Good Luck.