Your site will work with or without the "www" at the beginning. The "www" prefix is not required and many websites no longer use it. Here's more information on this topic.
It is up to you if you want to use www.yoursite.yolasite.com or yoursite.yolasite.com. Type in either one and you will get to your site. However, all URLs must have http:// or even better, https://. If you don't type this in your address bar, your browser will add it for you.