Hello Ishwar
JEE Main exam is a National level engineering entrance exam and is conducted for admission to NITs, IIITs, GFTIs. JEE Main is also the qualifying exam for JEE Advanced. JEE Advanced is the exam for admission to IITs.
Exam pattern of both JEE Main and Advanced is different. JEE Advanced is structured differently than the main exam.
Duration of JEE Main exam is three hours and consists of 90 multiple-choice questions. The exam consists of three sections: Physics, Chemistry, and Mathematics. Each section contains 30 questions. All sections are weighed equally.

For each correct answer, four marks are awarded. For each incorrect answer, one mark is deducted. No marks are awarded or deducted for unanswered questions.

JEE Advanced exam covers the same three topics Physics, Chemistry and Mathematics. However, unlike the main exam, the advanced exam is divided into two three-hour long papers, each divided into three sections (one for each topic). Go through the link to check the detailed JEE Advanced exam pattern- https://engineering.careers360.com/articles/jee-advanced-exam-pattern

For the detailed syllabus, go through the links below
JEE Main Syllabus- https://engineering.careers360.com/articles/jee-main-syllabus

JEE Advanced syllabus- https://engineering.careers360.com/articles/jee-advanced-syllabus

Hope this helps.
Good Luck!