The Website URL is where your visitors will first arrive on before being redirected away to another website or page.
For example, if you need to redirect mywebsite.com to mywebsite.ca for Canadian visitors, then the website URL will be mywebsite.com
Use your domain name if you plan to redirect your entire website or use a particular page URL if you plan to redirect only that page or its all its sub pages.
For example if you need to redirect mywebsite.com/blog and/or all its sub pages, then the Website URL should be mywebsite.com/blog