Here I am providing you the article given below for JEE Main Entrance Exam syllabus.

https://engineering.careers360.com/articles/jee-main-syllabus

The questions will be asked as per the syllabus.

You Can also prefer the previous year papers to know the level of the question & do practise as much you  can.

Good Luck!

Hello,

You should be prepared for JEE Main & JEE Advanced also.

Your basics in Physics, Chemistry & Mathematics should be very clear upto 12th std. You should read the NCERT books for basics. Then HC Verma for Physics, RD Sharma for Mathematics, OP Tendon for Physical & Inorganic Chemistry, and Organic Chemistry of "Arihant Publication" for detail or extra knowledge. 
You should also try to solve the previous years question papers, this helps too much and you should also give the mock test to rectify yourself and build your confidence level.

For more preparation tips, importants topics, syllabus & books, you can go through the link given below

Https://engineering.careers360.com/articles/jee-main-2019

Tahnks for query

All the best.