Developing A Social SharePoint Hosted App With Social REST

Once you know about the end points associated with Social data, Developing Social Apps become too easy.
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

'use strict';

var context = SP.ClientContext.get_current();
var feedManagerEndpoint;

// Get the SPAppWebUrl parameter from the query string and build
// the feed manager endpoint.
$(document).ready(function () {
    var appweburl;
    var params = document.URL.split("?")[1].split("&");
    for (var i = 0; i < params.length; i = i + 1) {
        var param = params[i].split("=");
        if (param[0] === "SPAppWebUrl") appweburl = param[1];
    }
    feedManagerEndpoint = decodeURIComponent(appweburl)+ "/_api/social.feed";
    postToMyFeed();
});

// Publish a post to the current user's feed by using the 
// "<app web URL>/_api/social.feed/my/Feed/Post" endpoint.
function postToMyFeed() {
    $.ajax( {
        url: feedManagerEndpoint + "/my/Feed/Post",
        type: "POST",
        data: JSON.stringify( { 
            'restCreationData':{
                '__metadata':{ 
                    'type':'SP.Social.SocialRestPostCreationData'
                },
                'ID':null, 
                'creationData':{ 
                    '__metadata':{ 
                        'type':'SP.Social.SocialPostCreationData'
                    },
                'ContentText':'This post was published using REST.',
                'UpdateStatusText':false
                } 
            } 
        }),
        headers: { 
            "accept": "application/json;odata=verbose",
            "content-type":"application/json;odata=verbose",
            "X-RequestDigest": $("#__REQUESTDIGEST").val()
        },
        success: getMyFeed,
        error: function (xhr, ajaxOptions, thrownError) { 
            alert("POST error:\n" + xhr.status + "\n" + thrownError);
        }
    });
}

// Get the current user's feed by using the 
// "<app web URL>/_api/social.feed/my/Feed" endpoint.
function getMyFeed() {
    $.ajax( {
        url: feedManagerEndpoint + "/my/news",
        headers: { 
            "accept": "application/json;odata=verbose"
        },
        success: feedRetrieved,
        error: function (xhr, ajaxOptions, thrownError) { 
            alert("GET error:\n" + xhr.status + "\n" + thrownError);
        }
    });    
}

// Parse the JSON data and iterate through the feed.
function feedRetrieved(data) {
    var stringData = JSON.stringify(data);
    var jsonObject = JSON.parse(stringData); 
     
    var feed = jsonObject.d.SocialFeed.Threads; 
    var threads = feed.results;
    var feedContent = "";
    for (var i = 0; i < threads.length; i++) {
        var thread = threads[i];
  
        var participants = thread.Actors;
        var owner = participants.results[thread.OwnerIndex].Name;
  alert(thread.RootPost.Text);
        feedContent += '<p>' + owner + 
            ' said "' + thread.RootPost.Text + '"</p>';
    }  
    $("#message").html(feedContent); 
}

Also  to get the feeds for particular user, REST Url can be queried as follows.

https://siteurl/_api/social.feed/actor(item='abc@abc.onmicrosoft.com')/Feed

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)