To open a web page, or URL (if the contact has one), click the "Open Web Page" 
button, or use a menu option, or simply click the hyperlink in the Contact Details. The program will open the web page in your default web browser.
When a contact card has more than one web page, you will see a drop-down list where you can select the desired one, for example:
This option is disabled when the selected contact does not have a web page.