Areas are small function units consists of Controllers, Views and models. Assume as scenario where we have two roles lets say, User and Admin. We know that these two roles require different views on website and hence different functionality. Admin has full control and user can only view or add comments on a post. This scenario require to have a separate area for Admin where we can manage its own functionality and UI.
In Asp.net dotnet5 we can add area by right clicking on project and click on Add and select Area. And from routing point of view its very important to configure area correctly.
For complete project checkout Asp.net Dotnet5 Blog Engine https://github.com/musmanrafiq/BlogEngine