Sitefinity content (including custom module content) is managed separately in Sitefinity. The Page only holds the widget to display
To manage the items themselves, you should use the Content
menu in the Sitefinity admin and select the content type you wish to manage (News, Events, etc), as shown here: Using the content modules
. Any custom modules you create will also show up in this list.
There you will be shown all the items of that type and can create, edit, or delete them as needed. Any changes you make will be reflected on the public page through the content widget you placed there.
Hope this is helpful!