1. JEE Mains is conducted by NTA for admission to NITs, IIITs, CFTIs as well as other engineering and technology institutes run by the state governments and private institutions while JEE Advanced is conducted by IITs for admission in 23 IITs in the country.

2. In JEE -Main, your speed, basic concepts are checked, while in JEE-Advanced, your concepts are challenged at an advanced level.

3. JEE-Main- Basic knowledge of chapters and 12th Board topics is enough to clear, JEE- Advance-Depth Knowledge of Topics  with Crystal Clear Concept on every topic with Accuracy and Speed.

All the best for your exam.

I hope this helps.