New AEM Page vs New Site
"New Site" is used to create a site from an existing Blueprint . Blueprint is part of the AEM Multi-Site Manager (MSM) functionality. The project is used to create several sites with a common structure, for example MySite in English, French, Spanish, etc.
The picture is created from an existing site. A site is a collection of pages, so you will be using New Page to create your site.
So, if you don't already have MySite , you will use the New Page option. When "MySite" is ready and you want to create copies of "MySite" for different languages โโand countries to provide a common structure, you will need to use the "New Site" option.
You can read more about the capabilities of AEM MSM here:
http://dev.day.com/docs/v5_2/html-resources/cq5_guide_power_user/ch13s04.html
http://dev.day.com/docs/en/cq/current/administering/multi_site_manager.html
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