The terms and conditions sections encompasses the terms of services that should be followed by each and every user of the wall post. Yes, it is mandatory to follow all the terms in order to ensure yours’ and others’ safety as well in wall post.
While registering, if it says email already exists then that means you have already registered once and you might have forgotten. In order to retrieve your old details you can contact us here.
While registering if it says username already existing, then it implies someone else has already taken the username you entered. In such case, you need to enter a different username that is available.