What's the difference between "Site ID and Community Name"
Site ID - Your Site ID is basically your username and is limited to standard characters, numbers, hyphens and underscores. Capital letters are not allowed.
Community Name - Your Community name can either be your Site ID name or something entirely different - It's entirely up to you. However, the benefits of having a different community name are that you can use spaces, non standard characters, or even have your name written in Japanese. Basically, it just allows you to have a more creative and fun name. :)