Hey there

For JEE mains you have to fill jee mains application form separately and appear for the exam. Joint Entrance Exam Main is the national level computer based test conducted by the National Testing Agency for the purpose of admissions to the undergraduate engineering courses in top engineering institutes in India like National Institutes of Technology, IIITs and the Govt funded Technical Institutes. In addition, it is also the screening cum qualifier test for JEE Advanced.  The test is held twice in a year in January and April, and validity of the result is one year.

Its is of 3 hours test and 4 hours for persons with benchmark disabilities you will be asked only from PCM for paper 1.

check the link

https://engineering.careers360.com/articles/jee-main-exam-pattern

good luck