The Text Pointer tool (symbolized by an A and arrow) allows you to add a text box with a pointer to an item in the image. Click to draw the box as normal, then click again on the item it should point to. The background of the box will remain transparent, but the box itself will remain visible.
The Text tab in the Text Pointer properties dialog allows you to set the text contents of the box, along with color and alignment options.
The Pen tab in the Text Pointer properties dialog allows you to set options for the width, color, and style of that box.
The Brush tab in the Text Pointer properties dialog allows you to set the type and color of the brush that will fill in that shape.
The Font tab in the Text Pointer properties dialog allows you to set the font for that box.