why the M1 is 001, M2 is 011 , M3 is 101 , M4 is 111 ? how do we know that ? And what is minterms and maxterm for Boolean's Algebra ? i read a lots of online notes , but i still cant understand it. Can anyone here helps to explain?

Those are binary values. The "M"s are M1, M3, M5, and M7.
They are not M1, M2, M3, and M4 as you stated.
They are not M1, M2, M5, and M7 as misstated in the problem.

They are simply the binary representations of 1, 3, 5, and 7 resp.