Firstly you have to choose from which college or institute you want to pursue B.tech.  Also you have to fulfill the eligibility criteria

• Candidate must have completed 10+12 from a recognized institute and scored minimum 60%
• Candidate must have completed 12th with subjects Physics, Chemistry and Maths.
• Candidate have to appear in entrance exams - JEE Mains, JEE Advance. To get admission in IIT you need to qualify both these exam
• AP EAMCET, TS EAMCET, MHT CET, KCET, WBJEE, KEAM are other state level exams . Also there are exams likeVITEEE, BITSAT which is compulsorily needed to be qualified for specific colleges. Some colleges like HNBGU needs CUET.
• After qualifying JEE Mains or Advance you need to participate in Joint Seat Allocation Authority (JoSSA)  counselling process to get into IIT ,NIT, and other counselling processes with respect to College.
• You get admission letter if selected after this step.