Ok. start by reading the manual, it will give you some understanding of the basics.
Then create a png file for your text. In a photo editing application, create an image with a transparent background. Put your desired text in it. Export this image as a png file with transparency enabled. Put this file in one of the subfolders where fpscreator is installed. For example in the files\texturebank\user or files\videobank. Just make sure you remember it.
Now you have to decide at what point you want the text to show up and attach it to the story zone marker or to a trigger zone by creating a small script.
To do know how to do this, you really need to read the manual and some of the scripting tutorials found on the forum here (FPSC Scripts section), to get a good understanding of what FPSC is all about and how to accomplish basic, simple tasks like these.
FPSC is way to cool, you can create even more then a fps with it!