What is JD (Jurist Doctor) Exactly?

I am actually at the last year of high school, and (Aiming Law), I am aiming at Harvard Law School, but I have heard they only give post graduate programmes (LLM) and something called JD (Jurist Doctor), which is a prerequisite for LLM there So what is JD exactly? Is it done after LLB? Or is it a substitute of... show more I am actually at the last year of high school, and (Aiming Law), I am aiming at Harvard Law School, but I have heard they only give post graduate programmes (LLM) and something called JD (Jurist Doctor), which is a prerequisite for LLM there

So what is JD exactly? Is it done after LLB? Or is it a substitute of LLB?
Also, assuming I do not live in US, what are the requirements for doing JD/LLM in Harvards
Do I have to get a LLB degree first? Or even if I could go directly into JD programme, do I have to give the following tests:-
1. SAT
2. LSAT
3. TOEFL
4. Advanced Placement

I live in India by the way
Thank You for your Answer!
Update: Also, are there any co curricular activities, or experience I need to have? For example any social service, or having learned different language or taken martial arts? I have taken class but not won any competition
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