Click on an object's edge or face, move your mouse, and click again to place a leader line with a text box. Screen Text:

Go to Tools > 3D Text (or click the 3D Text icon if visible). Settings: Enter Text: Type your desired phrase in the dialog box.

SketchUp Version 6 (the first version released under in 2007) and creating "proper" or standard text, you generally have three main options depending on whether you want labels, 2D notes, or 3D geometry. 1. Standard Text Tool (Labels & Notes)