Every SmartArt graphic contains a Text pane, which you can choose to use or not. The pane is for typing the graphic's text and for making other types of edits to the graphic. You can also work directly in the graphic.
As is shown in the picture:
The Text pane sits to the side of the graphic.
You type your text in the pane.
The text appears automatically in the corresponding shape in the graphic.
Notice that the graphic comes with default text so that you get a sense of where your text will go.
If you find it frustrating to select and work within the shapes in the graphic, you'll welcome the Text pane. No more fiddling with shape selection in order to type — just focus on and work with text without being distracted by the graphic.
By contrast, if you prefer to type directly into shapes in the graphic, do that. Or go back and forth, as it suits you.
In any case, the Text pane is handy if you've got lots of text to put in, or if you want a space for organizing text. You can also manipulate (add, delete, and move) text and shapes by working from the Text pane.
Accessibility benefit If you use a screen reader, the Text pane gives you a way to read and create a graphic on a slide, as long as you're in editing view.