First of all, the LW player is not a good player - you'd probably find it a lot easier to disable it (tools > options > player) & use another player

But if you do want to use the LW player then here's some basic playlist info.

Go to your library. To add files to a playlist, you can either highlight the file & click Enqueue or highlight the file & drag it down into the playlist area.
Once you have the songs that you want in the playlist, double click on the first file to launch the playlist.

If you want to save a playlist, click on Save As > browse for the location where you want to save the playlist > name the playlist > click Save.

To open that playlist again, click Open. If the playlist doesn't show, browse for the location where you saved it (playlists will have a .m3u extension), highlight the playlist > select.

If you've forgotten where you've saved playlists, or forgotten the names of playlists, just use your computer's search. Search all files & folders for .m3u... then your playlists should show.