Hello aspirant!!

You need to get qualified in JEE Mains and then you can appear for JEE Advance, which is an entance exam for IITs. You need to get good rank in JEE Advance to get in Top IITs like IIT Madras. 

Go through the below link to know the cutoff rank for your category in IIT Madras.

https://engineering.careers360.com/articles/jee-advanced-cutoff-for-iit-madras

Hope this helps you :)

Good Luck!!

Thank you.