Following example shows , how to get the feed activity of the current user and by the people and content user is following
To create this App, Open up new Project in Napa and click App.js
and add the following snippet
Also to get the feeds for particular user, REST Url can be queried as follows.
Read more about working with Social Feeds
Make sure that following permissions are granted to SharePoint App
This is very helpful REST API (End Point) reference for Social Data
And Tutorial for using Social REST API for following contents (Requires office 365 developer site)