First of all, you have mentioned nothing about the exam for which you have asked the question. Now, if I presume you asked about NITs and IITs you have to appear in JEE Mains for NITs and JEE Advanced+JEE Mains for IITs and pass them with a good rank.

But if you just want to do Btech than there are many good private colleges in our country that give admission on your class 12th marks.

Above all, I must suggest you to pursue engineering as an career option if and only if you like it else explore the world and find the most suitable field for yourself.