Activating a C00/Demo package is very easy and doesn't require a rap file. It can be done using ReActPSN or PSNPatch.
ReActPSN : Run the homebrew while pressing and holding circle on your controller.
PSNPatch : Run PSNPatch and press R1. It should displays a list of the games that have been unlocked.
Activating a package using a rap file requires few steps. It can be done with ReActPSN or PSNPatch. However, I will only describe how to do it with ReActPSN.