What is #include<iostream> for and why do I need to know it?

Question

I have been studying c++ and I don't understand it. I used the lesson from Sololearn and I still don't get what it is for. I also don't get namespace std.

Answer 1

It's a header file. Without including it you couldn't access the classes implemented in there.
iostream is inherited by istream and ostream and these contain the methods cin + cout which you probably use a lot