To create a playlist, just select any video you wish to add to the new playlist (right click it or swipe down on the video).
Then select the "Add to..." button in the right hand side of the player bar.
Select "New Playlist"
Enter the Playlist title. You can also check the checkbox if you would like the playlist to be private. This means that other YouTube users will not be able to see the playlist when they look at your profile.
Hit the "Create" button to create your new playlist. Done!