What computer operating system is your Premiere Elements 13 running?
You could be missing the Green or Blue Screen keying effects
a. You are in the Quick workspace of Premiere Elements 13 Windows - Solution go to Expert workspace fx Effects/Keying/
b. You are in Premiere Elements 13 Mac which does not offer Chroma Key, Green Screen Keying or Blue Screen Keying effects - one solution, use Difference Matte Keying effect.
Please let us know what of the above applies to your situation.
Add On. If you have not updated 13 to 13.1, please do that using Help Menu/Updates in an opened project.