The Text toolbar lets you see and edit the Text attributes of the current selection.
The Text toolbar
If the current selection does not use Text attributes, the Text toolbar is disabled.
If the current selection contains different Text attributes (e.g. bold and regular text), then the attribute that is different will be displayed with a mixed-value appearance (e.g. the Bold button turns light gray meaning some text is bold and some is not). You can then select a new attribute to be applied to the entire selection.
If no objects are selected, the Text attributes reflect the style to be used when new text is added.
More:
Align Left, Center, Align Right