Hey Ayush.

NLUs or National Law Universities are law colleges that provide five year integrated courses of Law

There are 2 types of Law courses in India- 3 year LLB course and 5 year integrated law course. 3 year law courses are for those who have completed their Undergraduation. So after completion of any 3 years of Undergraduate  course, you can do LLB which will be for 3 years. Hence It would take 6 years if you start with a separate UG degree. And in 5 year law course are for those who are seeking to puruse law after class 12th. It combines an Undergraduate degree with law, for example- BA LLb, BCOM LLb, BBA LLb etc. It takes 5 years after 12th class.

Admission in Nlus is through entrance called CLAT.

NLUs offer only 5 year law courses. Though you will be eligible to apply for NLUs even after graduation but it will lead to you wasting 2 years. You'll have to do a graduation degree again and it will take you 5 years to complete law where you can easily compelete it in 3 years. So after graduation 3 year LLB is more suitable.  Admission to various colleges is done through their own entrance exams or procedures. Here is a list of law entrances for 3 year LLB course -  

DU LLB - Delhi University  

MH CET- GLC mumbai, ILS Pune and other colleges in Maharashtra  

SLAT- Symbiosis Law school  

PU LLB- Panjab University, Chandigarh    

LSAT- Jindal global Law school, IIT Kharagpur and other private law colleges

BHU LLB- Banaras Hindu University 

BVP LLB- Bharatiya Vidyapeeth

TS LAWCET Etc

Best of luck!