This tutorial shows how to add text boxes to your map.
Select Insert then Shape.
Select the Text Box tool.
Click on the slide where you want to place the text box.
Click and drag down and right to create a box.
Release your mouse when the box is at the required size. 
To add text, right-click in the box and select Add Text.
Type your text.
Resize the text box by click and holding the bottom right corner, and dragging as needed.
Select the text in the box and use standard font settings to change the text font and size.
To move the text box, click and hold on an edge and clicking/dragging to the new position.