it will extend the template that it gets from the entity's cms.Page {% extends entity.get_template %}
the site template in its {% block main_page_body %} will thus include the file that view has specified, containing the special stuff for that view: {% include main_page_body_file %}
so, anything in your template that should not end up in pages like contacts and people should be inside {% block main_page_body %}
Need to explain: