To add a page simply edit the page you're are working on and then on the nodes link add a new node...
1) Create content
2) Select existing content to link it (if the original content is updated your sub-page will be updated too)
3) Select and clone (an exact copy of the original page is created in your site). If the page has sub-pages in the original site those too will be cloned, if the page has linked pages from other sites the links will be copied and relinked with your site)
For 2 and 3 please make sure the sharing policy on the pages you would like to link or clone are set to sharing and you have access to the site you'd like to pull content from.
The dependant node tab shows you, which pages are linking to the current page. This can be helpful if you are editing a page which is linked to multiple pages or the site you are working on or even to other sites.
You can link pages from any Site on a Fleamarket page.
The Fleemarket page is visible to the community of the existing site.
The permissions of the linked pages do not change when linking them.
I.e. if you create a Fleemarket on Sita A and embed a Public Page from Site B (this only works if she is sharable)
Then the page shows up for everyone.
If you create a restricted fleemarket on site A and link public content there, it is not visible because the fleemarket page is not public.
If Site A creates a Fleemarket with restricted and embeds another Restricted Page from another site and the user would have accessed it on both sides, it will show up.
To edit content from a different site you can access the direct link in the page overview. Click on the top left square and select from the drop down.
You can only edit pages you have access right to.