Liking a video is a quick way to let a video creator know that you enjoy their work. If you're signed in, liking a video will add it to your "Liked videos" playlist.
If you’re not the biggest fan of a video, disliking is one way to show your opinion. Keep in mind that if you want to report inappropriate content, you should report the video instead.
After December 5, 2019, your public “Liked videos” playlist will be made private, which means only you can see this playlist. You can still like videos, and videos will still show the number of likes.
under the video player. To dislike a video, use thumbs down 
. To undo your choice, simply select the icon again.
Remove from Liked videos 
.