Hello sudhir kumar.....
Your intrest towards btech is quite good.
As you mentioned you completed your 12 then you can write a number of entrance exams for the admission in engineering courses in various colleges.
Some of them i am mentioning below

• Jee main
• Bitsat
• Viteee
• Kl university entrance exam
• Tseamcet
• Apeamcet
• Tnea
• Amrita university

For all of them most of the syllabus is common and almost same but differ in exam pattern .
For more details about the exama after 12 visit
https://engineering.careers360.com/exams

All the best.....