JEE Mains and JEE Advanced have some differences though they are inter connected with each other.
They have differences in terms of syllabus, paper pattern, accepting Institutes etc.
You must check out – Difference Between JEE Mains and JEE Advanced
Number of attempts are also different for both exams – For JEE Mains students can apply for 3 years and candidates can appear for JEE Advanced only 2 consecutive years.
The main difference between both examinations is difference in their accepting institutes. Through JEE Main candidates get admission in NITs/IIITs/CFITs on the other hand IITs and ISM Dhanbad provide admissions through JEE Advanced.