I am trying to run some d3js on my MVC 6 and was looking at this example https://github.com/DustinEwers/D3-DotNetMVC-Demos/blob/master/D3Demos/Views/TagDemos/BasicBarChart.c
It's a bit more complicated now, but the documentation explains it quite well:
The ASP.NET MVC 5 starter web template utilized ASP.NET’s built-in support for bundling. In ASP.NET MVC 6, this functionality is better performed using client build steps...
So to bundle scripts together you can use a tool like gulp-concat. And to include a script, just add it in the way you would if it were static content:
For a more complete example of including content, the answer by @Shyju is excellent.