Build Actionproperty to
Copy to output directoryproperty to
Copy if newer. They will then be copied to the output folder, wherever that may be, during the Build process and you can access them in code by referring to the program folder as the root path, e.g.
Application.StartupPathin WinForms. I'd probably suggest adding a folder to your project and adding the files under that. In that case, the folder will be copied to the output as well, so account for that in the path you use at run time.
Properties.Resourcesin code. Depending on the type of data, you may get an object that you can use directly or a stream that you can write to a file or an object. The main advantage of resources is that the user cannot edit or delete them as they can with separate files.
var filePath = System.IO.Path.Combine(Application.StartupPath, "Song.mp3");
Environment.GetFolderPathto get the paths of various well-known system folders, e.g. the current user's Documents folder.