Hello aspirant,

Nptel is the online website launched by government of India with the help of IITs with the aim to deliver the IIT education to the non IITians students and get certified by the IITs in different courses. In this there are different courses for different branches offered by NITs where you can enroll for free and watch all the videos and atlast if you want to get certified then you have to give a exam by paying a amount of around 1000-1500 rupees and if you successfully clear the exam you are awarded a certificate by IIT.

Hope this helps

If any queries feel free to ask

All the best !!

Regards