When Apple released iTunes 11, many users complained that the more simplistic looking interface hide some of the most useful things like the sidebar and the main menu bar.
You can still have the sidebar displayed on the left of the screen, just follow this simple steps.
First, you need to show the main menu bar. Click on the upper left button and select Show the menu bar. You can use the Crtl+B keyboard shortcut as well.
In the Menu Bar, select Visualization and click on Show Sidebar. You can use the Ctrl+S shortcut.
This will show the sidebar permanently as in previous versions. You can always hide it using the keyboard shortcut or selecting the options within the Visualization menu.