When you are creating your site, you can choose what will be your domain name. You can use Uscreen's domain, which will have the name of your choosing with .uscreen.io attached at the end. If you would prefer to have a custom domain, please read this guide.
To change your domain name, navigate to Settings, go to Domain Settings, click Use different domain, then Select the option Uscreen Subdomain. Lastly, add the Storename and click Connect and then Continue. If the name is available, it will be saved as your URL.
It would be best for your site's name and domain to match so users can find it easily. Read the article "Rename Your Site" to change your site's name.