Hey,
Different NLU have different admission procedure
So I'm telling you about NLU Delhi

NLU Delhi offers various courses like 5-year integrated course B.A. LL.B. program
Admission to these courses is based on the scores in AILET

Eligibility criteria:

Candidates who aspire to take admission in B.A. LL.B. must have passed 10+2 or equivalent with not less than 50% marks.

Admission to the first year of 5-year B.A. LL.B., other than for Foreign Nationals, is made based on the merit in AILET entrance exam.
Applicants must secure at least 40% marks (30% marks for SC/ST) to be eligible for admissions.

You need to prepare for AILET entrance exam.
As admission is through this exam.
So start preparing for that .
All the best