"Login with Panterzone" is a sign-in button on some partner sites. Clicking it signs you in there with your existing Panterzone account, without setting a new password. The partner site never receives your Panterzone password and gets no access to your Panterzone session.

Before the first sign-in you see a consent screen naming the partner site and stating, in plain language, what it will receive, for example "Your email address". Only after you confirm does it proceed. On later visits to the same partner site, that confirmation does not need to be repeated every time.