There are two ways that you can add videos to a playlist:
1. Create/Select a playlist when you upload videos
1). Create a playlist
Enter the playlist name, then click "Create a new playlist"
2). Select a playlist
Click the playlist name that you want to add videos, you can also enter the playlist keywords to search playlists.
2. Add to a playlist in video detail page
Click "Add to" button, then select "Playlist"