Hello Bishal!

Admission into B.Tech course can be taken in a variety of ways as described below:

• There are many entrance exams for India's engineering colleges. But the major exam of all of them is JEE Mains. It is a national level examination. JEE Mains scores are accepted by many intstitues including  the 31 NITs, GGSIPU (since 2019) etc.
• If you get the required qualifying marks in JEE Mains, you can also sit for the JEE Advanced which is the entrance test for admission into the IIts.
• Further, there are many state level exams held by the state boards for admission into engineering colleges of their respective state. For example WBJEE, KCET, MHT CET etc.
• Also, many private institutes conduct their own entrnce examination. For example, Birla Institute of Technology and Science conducts BITSAT for admission ito B.Tech. courses. This also is a national level exam.