When a SiteWorks site is created your u3a is asked to specify a subdomain name of your choice. If your u3a is Anytown u3a then for SiteWorks it will most likely be anytown.u3asite.uk. The name cannot be changed. The prefix www is optional but no longer useful. Like all secure sites the prefix is https:// i.e. https://anytown.u3asite.uk