First take a look at this article
Bundling is a new feature in ASP.NET 4.5 that makes it easy to combine
  or bundle multiple files into a single file. You can create CSS,
  JavaScript and other bundles. Fewer files means fewer HTTP requests
  and that can improve first page load  performance.
The request 
http://localhost/MvcBM_time/bundles/AllMyScripts?v=r0sLDicvP58AIXN_mc3QdyVvVj5euZNzdsa2N1PKvb81 
is for the bundle AllMyScripts and contains a query string pair
  v=r0sLDicvP58AIXN_mc3QdyVvVj5euZNzdsa2N1PKvb81. 
The query string v has
  a value token that is a unique identifier used for caching. As long as
  the bundle doesn't change, the ASP.NET application will request the
  AllMyScripts  bundle using this token. If any file in the bundle
  changes, the ASP.NET optimization framework will generate a new token,
  guaranteeing that browser requests for the bundle will get the latest
  bundle
This is how to add directory with files
bundles.Add(new StyleBundle("~/jQueryUI/themes/baseAll")
    .IncludeDirectory("~/Content/themes/base", "*.css"));
This is how to add multiple files:
bundles.Add(new StyleBundle("~/Content/themes/base/css").Include(
          "~/Content/themes/base/jquery.ui.core.css",
          "~/Content/themes/base/jquery.ui.resizable.css",
          "~/Content/themes/base/jquery.ui.selectable.css",
          "~/Content/themes/base/jquery.ui.accordion.css",
          "~/Content/themes/base/jquery.ui.autocomplete.css",
          "~/Content/themes/base/jquery.ui.button.css",
          "~/Content/themes/base/jquery.ui.dialog.css",
          "~/Content/themes/base/jquery.ui.slider.css",
          "~/Content/themes/base/jquery.ui.tabs.css",
          "~/Content/themes/base/jquery.ui.datepicker.css",
          "~/Content/themes/base/jquery.ui.progressbar.css",
          "~/Content/themes/base/jquery.ui.theme.css"));