From this tab you can see the list PayPal verified emails. When there is a new payment request, the plugin sends an email automatically to the PayPal email address to verify it. Once the user clicks on the verification link, the email is added to the list.
However, you can also add an email manually clicking on the Add email button
You can configure the settings related to the PayPal verification from the General settings of the plugin, you can refer to this page.