If you've messed around with iTunes 11 in default view, you'll notice that creating a playlist has changed. If you have the sidebar turned on to make iTunes 11 look like earlier versions, creating a playlist is much the same as it was. But, if you have the sidebar turned off, Apple's Inside iTunes blog points out that there's a new dedicated area of iTunes just for making playlists.
To take advantage of playlist creation 2.0, turn off your sidebar if you have it on (Option+Command+S or View>Hide Sidebar). Along the top bar of iTunes, you'll see a new playlists button. Click this.
You'll move into a dedicated playlist window with your playlists on the left. Create a new one by clicking the add button (the plus sign) on the bottom left. You can choose from a basic playlist, a smart playlist or playlist folders. If you want to edit an existing playlist, click on the gear icon next to it. Here, you have options to edit, duplicate, delete, export or burn a playist to a disc.
If you want to create or edit a playlist, select that option and the playlist being worked on will slide to the right of the screen. Your library will now be on the left. Drag items onto the playlist, and name the playlist so you know what you're working on. You can toggle between songs, albums, artists and genre without being kicked out of the playlist view. Once you select videos, you'll go back to normal iTunes.