If you are shipping drugs through Fedex then you are pretty stupid so you should pay very careful attention. If this does not apply to you then please disregard.
Do not believe anything the police tell you. They may tell you that they are only interested in the person that sent the package. They may tell you that you will be helping yourself if you come clean. They may tell you things will get a lot worse if you do not cooperate now. Whatever they tell you,
shut up. You cannot possibly get in more trouble by not talking, and this is not something you can talk your way out of. If you are arrested, refuse to answer any questions until you have spoken to an attorney.