Enabling P4S Web Parts for Site Collections
Next, enable the new Web Parts for P4S in every site collection where users should be allowed to work with mashups or apps:
1. Log in as the administrator for a site collection. If needed, navigate to the parent site for the entire collection.
2. Click Site Actions > Site Settings.
3. Click Site Collection Features in the Site Collection Administration section.
4. Find MS4SP Web Parts and click Activate to activate these features or Deactivate to deactivate them.
This adds the Mashup Web Part and the App Web Part as valid Web Parts that users can add to Web Part pages. These Web Parts allow users to publish mashups and apps to SharePoint.