After 12th, you will get 2 options to get admission in one of the iit. If you want to go in engeneering stream then you want to go with jer main and advanced exam which is given as entrance exam for iit. After Clearing iit jee means jee advanced iit only invites you.
Jee advanced is one of the hardest exams in all over India because of its competition and the wast syllabus. So if you are completed 12th recently. Fill the form of jee main and start preparing for it. And once you will get cleared jee main then automatically you get selected for jee advanced.
And if you want to do bsc means bachelor of science then you need to simply complete the online form of any one iit. And if you are eligible then the iit will invite you. If you want iit jee syllabus comment us we will provide it.
If you want to crack iit i want to say you that by my own experience, you must study for minimum 6 hours for a year or if you are in 12th and you want to crack it then you must know some tricks to minimize your time in other activities and you must want to focus on your studies 100 percent.