A family of Microsoft word processing software products for creating web, email, and print documents.
The link provided by Mukherjee isn't working for me, so here's another (showing text boxes that are incorporated within SmartArt):
http://www.dummies.com/how-to/content/office-2011-for-mac-how-to-insert-a-smartart-graph.html
It should be basically the same in Word as in PowerPoint. You either click into the box where the text goes, or right-click on the border of the box and choose Edit Text or Add Text from the pop-up menu.