Excel 2007 has looks to match its muscles, including a new "uber-toolbar" called the Ribbon. The Ribbon was designed to enable fast access to the tools and functions you use most often.
A key benefit of the Ribbon is that it saves you from having to dig down into menus to access the tools you need. The odds are that, whichever tool you're looking for, it will already be on the Ribbon, rather than buried in some place requiring a heap of keystrokes or mouse clicks to get to.
If you do need access to a lesser-used function, get it through the Dialog Box Launcher. That's what the little arrow in the lower right corner of each command group is called.

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One thing you can't do in Excel 2007 that you could do (to excess) in prior versions of Excel is customize the toolbar, AKA the Ribbon. In prior versions of Excel, you could right click on a tool bar or menu, select Customize, and arrange your toolbars any way you wanted. However, with Office 2010, you will be able to customize the Ribbon.
Excel 2007 replaces this functionality with a way you can customize the Quick Access Toolbar. Try this customization, which will place the icon for any tool you want on the Quick Access Toolbar:
- Right-click anywhere on the Quick Access Toolbar.
- Select "Customize Quick Access Toolbar."
- Choose an icon from the left panel and click the Add button to install it on the Quick Access Toolbar.
- Click OK.

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You can place a lot of icons on the Quick Access Toolbar this way, so don’t over mourn the loss of the old anything-goes toolbars. You can also move the Quick Access Toolbar itself: left-click on its arrow, then click Show Above/Below the Ribbon.

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For a closer look at the Quick Access Toolbar, see Customizing and Adding Buttons to the Excel 2007 Ribbon.