Hey Anku! JEE Main and JEE Advance both are conducted by National Testing Agency (NTA), JEE Main is like a qualifying exam of JEE Advance through which a candidate get admission into IITs. The students qualifying JEE Mains are eligible for JEE Advance and JoSAA counselling. Hope this may help you. 

Hii aspirant..

JEE mains and JEE advanced are two different examinations. Although both will help you to get admissions at engineering colleges but the difference is that for giving JEE advanced exam first of all you need to qualify JEE mains exam. 

JEE mains exam is majorly for getting admission at NITS and other government funded technical institutes (gftis) but other than this there are many other colleges which accept JEE mains marks for taking admission. JEE advanced exam is for getting admission at IIT and for getting admission at IIT first of all one needs to qualify JEE mains exam and after qualifying JEE mains exam you will be eligible for JEE advance exam and then after qualifying JEE advance exam you are eligible to get admissions at IIT according to their respective ranks.

Hope it helps. 

Best of luck for your future.