The Text/Title effect works only when you position it over an exiting video or image. When you position it over an empty portion on the timeline, then the effect will not show any text.
Hence, to add Credits/Titles before or after your video, you must make sure that you position the effect over an image. You can easily create an image in Microsoftr Paint or your favorite image editor and use the image in the timeline before or after the actual video. Now position the Text/Title effect over this image.