Document Tabs work like tabs in other programs. They allow you to easily switch between open Photoshop files simply by clicking on the tab. You can reorder the tabs, or rearrange the documents inside your window by clicking and dragging on the tabs.
The Arrange Documents button on the Application Bar also allows you to change how your Photoshop files are arranged in the window.
Document Tabs are brand new to Photoshop CS4.
Photoshop panels give you even more options for your tools beyond the Control Panel. They can also allow you to choose colors and styles, undo many steps, see important information about your files, and do more complex editing involving layers, paths and channels. There are many other types of panels too. More seem to be added with every new version of Photoshop. To view any panel that is not currently visible, select it from the Window menu on the Application Bar.
Panels used to be called Palettes in earlier versions of Photoshop.
The Cursor is the form that your mouse takes when it is on the screen. The Cursor image changes its look inside the image window depending on what tool you currently have selected in the Tool Box.
For example, the Cursor looks like a little eyedropper when you select the Eyedropper tool. It looks like a paint bucket when the Paint Bucket tool is selected. In this image it looks like a cross hair, which is used for the Marquee tools.