what is the meaning of <<

Answer 1

The "<<" operator has different meanings in different contexts.

It's used as the "insert" operator for cout:
cout << "hello";

But it's also used as the "bitwise left shift" operator:
integer x = 1;
x = x << 3; // 1 becomes 8 because the bits have been shifted 3 times left.

Answer 2

It's the operator to send something to a stream object.

Answer 3

output in your screen