Hello dear

Credit system is just a system to calculate the knowledge and grades of the students.

I am explaining you with an example like. :

Suppose you have 5 subjects in your first semester

A, B, C, D and E out of these 5 subjects 2 subjects A and C are the core subjects and most important subjects and then D and E are not most important but important for your course and rest B is not much important and do not add much value to your existing knowledge. So NIT gives the credit to each subject like :

A- 3

B-1

C-3

D-2

E-2

And now you want to calculate your overall grade ( if it is grade system)

Than you will calculate your grades with formula:

[(Grade of A) * (credit of A) + (grade of B) *(credit of B)  + ............ + (grade of E) * (Credit of E) ]   ÷   [ credit of A + credit of B +........ + credit of E]

And grade decided on percentage score in that subjects like 10 for 90+ percentage

9 for 80to 90 percentage and so on( this grade criteria is also different for different college they decide their own criteria and range of percentage).

Hope you get it and if you have still doubt you are free to ask.

Good luck