The project.json file is the place where you add the dependencies with respect to your project. By default .NET Core loads only the necessary dependency/dnx, its quite different from the way the previous version of .NET(loads all dependency irrespective of usages).
Structure of project.json :
By default .NET Core loads only required dependencies in the project,to add reference or dependencies to project this is the place where you declare the references . It generally contains the dependency name and version.The packages are pulled automatically as Nuget Packages.
Specify the version of .NET being used,for instance .NET Core /.NET 4 etc..
This region will let you define what to include/exclude the items that are being published with IIS server.
This region specifies the build automation for scripts(like installing gulp,trunk etc..).All the commands defined in the scripts will be executed before the site get published in the server(prepublish).For instance “bower install” refers to install bower before publishing the package.