Hey, Utkarsh!

The prep ranks are for preparatory courses offered in IITs to students who belong to the reserved categories. In this, you are made to study English, math, physics and chemistry; successful completion of which, the admissions committee declares you as "pass" or as "failed" if otherwise. Once you have passed that, you can get a seat for BTech in that IIT from the next year, depending on the vacancy. For more information regarding the prep courses, you are advised to visit the following site: https://www.iitm.ac.in/preparatorycourse .

Also, you cannot get a college through that rank. You are just eligible for the preparatory courses.

Hope this helps. All the best!