You can add text quickly and easily to almost any AutoShape except lines. Do not draw an AutoShape and then create a text box for text. This creates two separate objects: the AutoShape and the text box, which will cause you unnecessary problems later when you need to move or resize the AutoShape.
To avoid any potential problems, simply select the shape you want to add text to and then start typing. It is almost too easy! The text is automatically centered in the AutoShape and can be formatted in the same manner as other text objects.