When viewing a song page if you click the "Add to playlist" checkbox of the song it will be added to your current playlist and this playlist will automatically be saved using a browser cookie so that you can reload your playlist when using the same computer and web browser. If you wish to save your playlist permanently so that it may be accessed from any computer, just choose a unique name for it and then save it using the "Save Playlist" form above or at the foot of any page.
Once you have saved a playlist you can then create another one if you so choose. You can create an unlimited number of playlists in fact! You can add and delete songs from your playlist by loading them, altering them and then saving them under a different name, as overwriting existing playlists is not permitted. From time to time you may find that a song does not play at all. In such cases you can just replace with a version that does play and then remove the
song(s) from your playlist and then resave it (under a different name).