You can create a playlist by selecting or adding a song, or you can create Liked Songs playlist by tapping heart icon you like on play screen.
Select songs you want from Songs list and tap the Add playlist icon at the bottom. You can add an existing playlist or a new playlist by creating it.
Add a song that is playing to the playlist
When you click the 'Add Playlist' button on the right side of the play screen, it is added to the playlist.
Create 'Liked Songs' playlist
If you tap ♡ Heart icon on the play screen, the 'Liked Songs' playlist is automatically created.