Excel 2007 user interface does not show the developer tab in the default display. If it is not shown in the ribbon then see How to show the developer tab in Excel 2007.
The developer tab consists of 4 groups:
The Code group gives you access to the visual basic editor. You can access your existing macros and write or record new ones. You can also setup macro security level (enable macros to run or disable them).
The Control group allows you to insert user controls, switch between design mode and normal mode, access control properties, view code within controls or run a dialogue (user form).
The XML group allows you to add, import or export XML maps into you workbook.
In the Modify group you can specify custom document information panel template (contains author, title, subject ..etc.)
Posts on Excel 2007 user interface: