You can download songs, albums or playlist from Spotify to listen to offline as long as they are in your light songs list or a playlist on.

Do you have a premium account?

Find the track you want from your playlist.

You can use the filter function to help you find a specific one.

Then click the download button at the top right side of your list on the song will start downloading.

You can also download whole albums or playlists by selecting them and then clicking the same download icon.