display files and folders

You could create a new instance of a FolderBrowser dialog and display it to the user when the form loads. However, the FolderBrowser only shows folders.

FolderBrowser browser = new FolderBrowser();
browser.ShowDialog();

Or if you are wanting to give the user the ability to select a file, show an OpenFileDialog.

OpenFileDialog openFileDialog = new OpenFileDialog()
openFileDialog.ShowDialog();

Just remember to get and set the current working path because in MS's infinite wisdom ( bless them :P ) they decided that they were going to change the applications working directory to the directory selected in the dialog and not give an option to opt out of it which could cause alot of problems later in the application. Try this:

private string GetFilePath()
{
    //Get the current path of the application
    string currentPath = Directory.GetCurrentDirectory();

    //Create a new dialog
    OpenFileDialog openFileDialog = new OpenFileDialog()

    try
    {
        //Show the dialog
        if (openFileDialog.ShowDialog() == DialogResult.OK)
            return openFileDialog.FileName;   //Return path
        else
            return String.Empty;   //Return an empty string
    }
    finally
    {
       //Reset directory regardless of dialog result
       Directory.SetCurrentDirectory(currentPath);
    }
}

That method will show an open file dialog, and if the user clicks OK, it will grab the file path that was specified and return it.