Hii

If you appear in MET- 2019 i.e Manipal Entrance examination, the scores would be valid only for admission into the campuses on Manipal University itself. Manipal University is a private deemed university. 
You can not use the scores of MET exam for admission to govt colleges.
For govt colleges, NITs, GFTIS, IIITs and other govt colleges you need to appear in JEE Mains exam. For IITs specially, after JEE Mains, you need to also appear in JEE Advance and qualify it.
For appearing in JEE Mains, you need to qualify class 12th exam with PCM and score a minimum of 50% in your exam. For getting into NITs, IIITs, GFTIs, you will require a minimum of 75% aggregate in your class 12th exam.

Hope this helps
Feel free to revert back for doubt.
Thanks!