I don't know whether u need #include < iostream >. Is it the beginning of any Programm?

Answer 1

If you want to use the functions of input and output: cout, cin... you should import them. They are written in the iostream library

Answer 2

Tanks :)

Answer 3

<iostream> is just a library that you can call in the beginning of your code to access specific functions in that library.This also works for other things like <rand> which gives you the rand function that can generate a random number.