You can ask questions and write a notebook entry for free. You only pay if you want a class with an informal tutor or a professional teacher. Also, your original question should read "I don't understand. Do I have to pay to write (to someone) in English?"

No. You can use this website for free. You only pay if you reserve a session with a teacher or tutor. Many of these are professionals, so please think about it. ;)

It isn't necessary. Just follow a random person from the community --> language partners and ask him/her for some English practice or maybe an exchange and velato! PS learning some Italian occasionally :)

No, you can chat with all people for free, but if you want to take formal clasess you have to pay for it...