Hai Sneha Patil,

 NPTEL is National Programme on Technology Enhanced Learning is a combined initiative by 7 IITs and IISC.Several courses are taught online by professors from IITs and IISC.You can select course based on your interest irrespective of your current branch you can select course you want to pursue.Also you can appear for certification exam by paying examination fee.As they teach concepts clearly it will be helpful for your gate and other competetive exams 

Hello Sneha

NPETL i.e National programme on technology enhanced learning is a platform which provides E- learning through their online video courses. They also provide various certification.

Now coming to that is it useful for various competetive exams like GATE or Engerring Services. Yes, if you are not taking any coaching classes and in 2nd or 3rs year of your couse then it can surely. 

The reason is becasue Videos are bit long and if you have so much time then not only you can build concepts but also make notes on your own.