Dear student,
You can take admission into engineering after successful completion of Class 12th with science stream. You must have to complete the class 12th with mathematics subject.

To take admission in IIT's and NIT or any top engineering college all over India you have to give JEE mains and Advance entrance exam conducted by National Test Agency.

There are some colleges which accept state level entrance test also.

The state from which you belong you can checkout the entrance exam for engineering at your state and appear to that exam.
Like
Maharashtra conduct MHTCET
AP Conduct EAMCET


Good luck