Hello aspirant

As per your query.you want to take a admission in iim. for this you have to qualifiy CAT.with good rank.for prepration of CAT.you can join a coaching .there are many coaching availabe .who prepraing for CAT exam.

TIMES is best coaching for CAT.

in this coaching .they will teach you  whole syllabus of CAT.

if you want to study in online.you can also do it.now a day many online course availabe in you tube .

you can follow leacture in unacademy

Thanku