C# Create new class properties ... things (I'm new.. very new)

public partial class Form1 : Form
{
    SoundPlayer player;
    Dictionary<string, Song> songs;
    Song selectedSong = null;

    public Form1()
    {
        InitializeComponent();

        songs = new Dictionary<string, Song>();

        // this allows you to select multiple songs from the 
        // songsListBox to add to the playListBox by holding
        // down the Ctrl or Shift key.
        songsListBox.SelectionMode = SelectionMode.MultiExtended;

        //allows multiple files to be selected
        // by holding down the Ctrl or Shift key.
        openSongDialog.Multiselect = true;
    }

    //add songs to the songsListBox
    private void addSongsButton_Click(object sender, EventArgs e)
    {
        if (openSongDialog.ShowDialog() == System.Windows.Forms.DialogResult.OK)
        {
            for (int i = 0; i < openSongDialog.FileNames.Length; i++)
            {
                Song song = new Song(openSongDialog.FileNames[i]);
                songs.Add(song.Name, song);
                songsListBox.Items.Add(song.Name);
            }
        }
    }

    //removes selected songs from the songsListBox and also the playListBox
    private void removeSongsButton_Click(object sender, EventArgs e)
    {
        if (selectedSong != null && songsListBox.SelectedItems.Contains(selectedSong.Name))
        {
            StopPlayback();
            selectedSong = null;
        }

        for (int i = songsListBox.SelectedItems.Count; i > 0; i--)
        {
            string selectedSongName = songsListBox.SelectedItems[i - 1].ToString();

            songsListBox.Items.Remove(selectedSongName);
            playListBox.Items.Remove(selectedSongName);
            songs.Remove(selectedSongName);
        }
    }

    private void playListBox_SelectedIndexChanged(object sender, EventArgs e)
    {
        if (playListBox.SelectedItem != null &&
            songs[playListBox.SelectedItem.ToString()] != selectedSong)
        {
            StopPlayback();
            selectedSong = songs[playListBox.SelectedItem.ToString()];
        }
    }

    private void playButton_Click(object sender, EventArgs e)
    {
        if (selectedSong != null)
        {
            player = new SoundPlayer(selectedSong.FullPath);
            player.Play();
        }
    }

    private void stopButton_Click(object sender, EventArgs e)
    {
        StopPlayback();
    }

    private void StopPlayback()
    {
        if (player != null)
        {
            player.Stop();
            player.Dispose();
        }
    }

    //adds songs selected in the songsListBox to the playListBox
    private void addToPlaylistButton_Click(object sender, EventArgs e)
    {
        for (int i = 0; i < songsListBox.SelectedItems.Count; i++)
        {
            // the if statement checks if playListBox already
            // contains a song with this name before adding it.
            if (!playListBox.Items.Contains(songsListBox.SelectedItems[i]))
            {
                playListBox.Items.Add(songsListBox.SelectedItems[i]);
            }
        }
    }

    //removes selected song from the playListBox
    private void removeFromPlaylistButton_Click(object sender, EventArgs e)
    {
        if (selectedSong != null && selectedSong.Name == playListBox.SelectedItem.ToString())
        {
            StopPlayback();
            selectedSong = null;
        }

        playListBox.Items.Remove(playListBox.SelectedItem);
    }

    //removes all songs from the playListBox
    private void clearPlaylistButton_Click(object sender, EventArgs e)
    {
        if (selectedSong != null)
        {
            StopPlayback();
            selectedSong = null;
        }

        playListBox.Items.Clear();
    }
}

class Song
{
    internal string FullPath { get; private set; }
    internal string Directory { get; private set; }
    internal string Name { get; private set; }

    public Song(string path)
    {
        FullPath = path;
        Directory = System.IO.Path.GetDirectoryName(path);
        Name = System.IO.Path.GetFileNameWithoutExtension(path);
    }
}

class Song
{
    internal string Name { get; private set; }
    internal string FullPath { get; private set; }
    internal string Directory { get; private set; }

    public Song(string path)
    {
        FullPath = path;
        Name = Path.GetFileNameWithoutExtension(path);
        Directory = Path.GetDirectoryName(path);
    } 
}

// * NOTE: openSongDialog is of the type OpenFileDialog *
class Form1 : Form
{
    List<Song> songs = new List<Song>();

    if (openSongDialog.ShowDialog() == DialogResult.OK)
    {
        Song song = new Song(openSongDialog.FileName);
       
        songs.Add(song);
    }
}

class Form1 : Form
{
    Dictionary<string, Song> songs = new Dictionary<string, Song>();

    if (openSongDialog.ShowDialog() == DialogResult.OK)
    {
        Song song = new Song(openSongDialog.FileName);
       
        songs.Add(song.Name, song);
    }
}

Song selectedSong = songs[songListBox.SelectedItem.ToString()];