How can we access SharePoint data in App using REST

REST in SharePoint 2013

CSOM: Client Side Object Model

WCF: Client.svc

In SP2010: Client.svc can access through Javascript, SIlverLight or .Net Code (Client Object Model) (_vit/bin/client.svc)

In SP2013: Client.svc is extended REST. 

So now we can access Client.svc using REST Services also.(_api/client.svc)

How can we access SharePoint data in App using REST

Site: http://server/site/_api/site
Web: http://server/site/_api/web
Search: http://server/site/_api/search
User Profile: http://server/site/_api/SP.UserProfiles.PeopleManager
SharePoint Social: http://server/site/_api/social.feed
Yammer: https://www.yammer.com/api
App Context: /_api/SP.AppWebContextSite(@target)/