How to organize the messenger of those. support through vkontakte?

Question

PHP

Hello. Today I came across one interesting messenger, like jivosite, Only it is organized through VK.
How can you do the same?
praktikum4u.ru/treningi/25-noyabrya-oratorskoe-iskusstvo-20-radislav-gandapas.html

Answer 1

Tyk

Answer 2

Oh my God, well, you write in the search box "messages to the site through Vkontakte" - in the first five results the answer! Five seconds of searching.

Answer 3

And what will site visitors who do not have a page in VK do?