Hello vivek
I like your curiousity for your future.
As you want to take a job in top companies like Infosys,google ,amazon it is not compulsary to have a degree from iit or nit but hailing from such institutes will benefit you.
As most of the top companies come to the placement drive in the iit and nit only so you can easily get placed.
But if you have great knowledge you can get job easily.
Some tikes the iitian tag matters (most of the times)
As you go into iits you will find likeminded people with you that brings new ideas in you ,that develops more creativity in you that is the only reason why iitians have more creativity.
Hope it helps you
All the best..