what is the use of classify model into Entity,Repository,Service

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MVC

C#5.0

As a beginner it is difficult to understand the flow how the mvc application is working.After i learned about the model,view and controller function i know the work flow of MVC.Now the model part is split up into entity,Repository and Service.whats my doubt is what are all the things that i put under the entity,service and repository.
If any one had any simple clarification with simple example please answer for my post.
if any related links are there just post the link also.