Answer 1

You just started C++, so even if I explain it to you, you won't understand. Continue Learning, and you will understand yourself.
Just a very basic, beginner, short explanation:
"#include" tells the compiler to include the <iostream> library in your program. <iostream> library is where the basic "functionalities" of C++ (cout, for example) is "stored".
However, this explanation is not so accurate, specific, or technical.