hi,

see you need to appear in jee main and jee advance exam in order to get admission in iist. iist admission is basis on jee advance score , also the qualifying marks criteria is you need to secure 75% aggregate marks in 10+2 if your are from general category, for sc/st candidates marks criteria is 65%. now you need to secure the cutoff marks in jee main in order to qualify for jee advance exam. jee advance is one of the toughest entrance exam of india, you need to study sincerely now and should practice mcq questions. you may follow tata macgraw books for jee main and advance preparation.