I want to participate in it, but I don’t know where to start? How do I register?
Yeah but do I need to make only an abstract or full research paper too? And what about the oral presentation?
http://www.jshs.org/guidelines.html
I think that you can find everything you need by poking around on this link.
To compete, you need to write a full paper and then make a presentation in front of judges. The time limit (12 minutes) is strictly enforced.
In my opinion, the judging is very subjective. They seemed to favor research topics in their own areas and generally asked very banal questions for presentations in areas that they weren’t familiar with. It appeared that the judges did not read the papers before the session. We got a fantastic breakfast before the competition though 
So I have to make oral presentation regardless of whether I advance?
Yes, you compete with 5-7 others in the morning in a session. The concurrent sessions each address one research topic (such as math). Each competitor in the session gives a presentation. At the end of the session, the judges (three in our case) select the one that they thought was best. Then, the winners from all of the sessions compete together in the afternoon, to see who advances to the national competition. In other words, the session winners give their presentations again, but this time to the full panel of judges. At least that’s how it was when my kid competed.
Are you such a cool guy that you don’t say thanks to people helping you out?
l
Thanks @whatisyourquest I found this helpful 