Article: It's the red square with a white play button inside. You'll usually find it in the app drawer. You can search for a playlist by tapping the magnifying glass icon. To find a playlist you created, tap Library, and then scroll down to the Playlists section.  It's the round icon with a downward-pointing arrow inside. This determines the picture and sound quality of the videos in the playlist. Choose Low, Medium, or HD.  The playlist is now available offline.

What is a summary?
Open YouTube on your Android. Find a playlist to download. Tap the playlist. Tap the download button. Select a video quality. Tap OK. Tap OK to confirm.