HI Girish.
After 12 th you can take admission directly in a law college and it will be a  5 year integrated course of B.A LLB or BCOM LLB or BBA LLB depending on which course a particular college offers.
And if you have already pursued your Undergraduation from a recognised university/ college, only then you will be eligible for a 3 year LLB course.
And CLAT is not mandatory admission in for either of the 2 courses.
Clat is only an entrance test for admission in the National Law universities which only offer 5 year  programmes and masters.
Their are other colleges/ universities which offer law courses like Delhi University, GLC Mumbai,  ILS Pune, Christ University, Punjab University, Chandigarh, Jindal Global Law School and many more. These colleges have their own entrances and admission procedures and you do not require to take CLAT for admission in these.
Here is a list of various law colleges in India
LIST OF LAW COLLEGES

Common Law Admission Test

Admit Card | Application | Eligibility | Exam Pattern | Preparation Tips | Question Paper | Exam Centre | Accepting Colleges

Get Updates Brochure