What John said. And to have it remain on the slide for a while before it
fades out, here's what you can do.
First, add entrance fade and exit fade onto the textbox.
Set both effects to Start: "After Previous".
Double click on the exit fade effect and click on the Timing tab.
Adjust the delay. The higher the delay, the longer the text will stay on the
slide before fading out.
Click ok to apply the change.