Indian Institute of Technology, Delhi

Yes, you have to qualify in one of the following exams in order to get into IIT. CAT: (Common Admission Test) to get enrolled into MBA programme at IIT Kharagpur, Madras, Delhi, Kanpur, Bombay and Roorkee.
GATE: (Graduate Aptitute Test in Engineering) for M.Tech courses at various IITs and IISc.
IIT-JAM: The Joint Admission Test is an admission test to Master of Science (M.Sc. ) and other post-graduate Science programs at the IITs and IISc.
UCEED : Undergraduate Common Entrance Examination for Design is an entrance exam for the admission in Bachelor of Design. Available only at IIT Bombay and Guwahati.
CEED : The Common Entrance Examination for Design (CEED) is a joint entrance exam for post-graduate studies in the field of technological design held annually jointly at all IITs and IISc.

Start your preparation as early as you can (from class 9th it is recommended but not mandatory because actual preparation stats from class 11th, class 9-10th courses are generally for your foundation) by either self-study or by joining a renowned coaching institute nearby your place.Forget about your past achievements (like class 9-10th CGPA, class 8th marks, etc.) and your past failures (like being average or anything else). Develop your study ritual and work ethics by starting studying for 6 hours a day and developing a habit of at least 6 hours. Self-study because without self-studies, JEE would just be a dream. Maintain your consistency, it is most important here. Don't give up on new exposure and mind screwing concepts, regular studies and tests. Please don't give up at this stage and maintain your consistency. Don't demotivate yourself by watching other candidates scoring more than you in any test, focus on your path and build your own story.