A playlist is a collection of musical tracks manually added by a user and played in a order determined by him. 

In the ARCHOS Music application be careful, there is a difference between the playlist being played and the one saved.

Currently playing playlist 

The currently playing playlist is temporary and changes everytime you do an action. You can display it by pressing  .

By default, when you play a track, all the tracks of the album / folder are automatically added to the currently playing playlist. If you then play the track of another album / folder, the playlist will change to only have the track of this album / library. 
To manually add items of your choice (track / album / artist) to the currently playing playlist, long press on the item and select Add to the playlist and then Current Playlist 

You can save the current playlist by pressing  (or the dedicated Menu button of your device) and then select Save as a playlist. 

Creating / Saving a playlist 

To add a track / album / artist to a playlist, go in your library and long press on the desired item. In the menu that launches , select Add to a playlist and New or select an existing playlist. 

By creating a new playlist, it will be automatically saved.