Office 2010 is overall very similar to Office 2007, but with a few changes:

"File" Tab: This replaces the Office Button, and clicking it brings you to "backstage view". Here’s a video from Microsoft showing "Backstage View". 

Other new Office 2010 features:

• You can now customize the ribbon by creating your own tabs.
• See a preview of your pasting options with "Paste Preview".
• Protected View Files downloaded from internet sources are read-only until you enable editing. This protects you from viruses.
• Files on servers can be accessed by multiple users. You won’t get locked out if someone else is editing.
• New picture and image controls, including artistic effects and background removal. 

New Features just in Word:

• Navigation Pane lets you easily navigate through long documents.
• Mark as Final option prevents changes to a final draft.
• Mini-Translator gives you on-the-spot translations and pronunciation.

New Features in Excel:

• "Sparklines" are miniature charts that live in cells.
• Improvements to pivot tables, including the introduction of "slicers" to filter data.
• Some functions have been renamed for greater accuracy.

New Features in Powerpoint:

• For larger presentations, you can organize slides in sections.
• Merge and compare presentations while collaborating.
• You can now embed and edit videos in your presentation.
• Insert youtube videos into a slide.
• Turn presentations into videos.
• Use your mouse as a virtual laser pointer.

Moving up from version 2003?

Watch these "getting started" videos for Word or Excel. They introduce the Ribbon and other changes. Then, use these interactive guides to see where items in the 2003 menus are now located in the ribbon.

Want to explore more? Visit Microsoft’s Office Support pages.