In Library, you can manage artists you are following, liked videos, and the recent history.
Following: You can see the Artist Channels you are following. If you want to stop following the artist, click 'Unfollow' in More button.
Liked: You can see the videos you liked. If you want to unlike the video, click 'Unlike' in More button.
History: You can see the videos you watched all in one page. If you want to delete specific videos, click 'Remove from watch history' in More button. If you want to delete all history, click 'Remove all' at top right.