why we need to use the streams insertion in the code?

Answer 1

<<cout output >>cin input

Answer 2

give an example

Answer 3

too show that you are using "cout" to print text, for example,
cout << a << " + " << b;
if "<<" is not used,
cout a " + " b; // unclear

Answer 4

cout << " hello world" ;

what is the benefit of this <<