ASP.NET Identity is the new membership system for building ASP.NET web applications. ASP.NET Identity allows you to add login features to your application and makes it easy to customize data about the logged in user.
One ASP.NET Identity system
ASP.NET Identity can be used with all of the ASP.NET frameworks such as ASP.NET MVC, Web Forms, Web Pages, Web API and SignalR
Ease of plugging in profile data about the user
When you create new users in your application, it is now easy to add extra information about the user. For eg.. if you wanted to add a Birthdate option for users when they Register an account in your application.
ASP.NET Identity uses Entity Framework Code First and it is possible to extend the POCO classes.
By default the ASP.NET Identity system will store all the user information in a database. ASP.NET Identity uses Entity Framework Code First to implement all of its persistence mechanism.
If your application requirements are that this information might be stored in a different storage mechanism such as SharePoint, Azure Table Service, No Sql databases etc. it is now possible to plug in different storage providers.
ASP.NET Identity makes the web application more unit testable. You can write Unit Tests for the parts of your application that use ASP.NET Identity
Simple Role provider
There is a Simple Role providers which lets you restrict access to parts of your application by Roles. You can easily create Roles such as “Admin” and add Users to Roles.
ASP.NET Identity supports claims-based authentication, where the user’s identity is represented as a set of claims. There is a Claims
You can easily add external logins such as Microsoft Account, Facebook, Twitter and Google to your application store the user specific data in your application using this system.
You can also add login functionality using Windows Azure Active Directory and store the user specific data in your application using this system.
For more detail I would suggest you visit the following page: http://www.asp.net/identity/overview/getting-started/introduction-to-aspnet-identity