JEE Mains consists of questions from Physics,Chemistry and Mathematics of class 11th and 12th. So,make sure you are thorough with the syllabus of NCERT.Each section will have 20 Objective questions having four options each with only 1 correct option and 5 Numerical questions with numerical value as answer. For MCQs - 4 Marks will be given for every correct answer and 1 Mark will be deducted for every incorrect answer
For answer with numeric value - 4 Marks will be awarded for every correct answer and 0 Mark will be deducted for every incorrect answer.
You can refer to the link given below for detailed information about the chapterwise weightage of Physics,Chemistry and Mathematics in JEE Mains:
Hope this helps.