Microsoft Office 2010 Service Pack 2 is a collection of fixes to resolve bugs and improve performance, security and reliability in Office 2010.
There are no new program options, and you won't see any changes in the interface. Instead the Service Pack is essentially a collection of previously issued Office Updates, with some previously unreleased fixes added for good measure.
This does make for a bulky download, some 730MB. If you need to update multiple machines then make sure you save the file locally rather than launching it directly from the download link.
Please note also that the Service Pack isn't supported for Windows 8.
If you need to know more about what's included in the Service Pack then the official Microsoft Support page has the details.
If you've missed out on Office 2010 updates for whatever reason then this is an essential download