Click on the Microsoft Office Button Excel Options Add-Ins  You can highlight the various add-Ins to get a brief description of what it does.

Make sure you have Manage: Excel Add-ins selected and click the Go… button and select the available Add-in from the resulting screen.

Click Yes to the confirmation screen.

Now just wait while Office installs the selected Add-Ins.  When finished you can click the Add-Ins tab on the Ribbon to start using them.

There are also third-party Add-Ins as well.  What are some of your favorites?