I understand having an emotional strength and an emotional weakness.

I understand starting at a morality of 50.

what I don't understand is how one pays for the extra xp and or credits one can get at character generation. can someone please explain this?

You don't. You choose either XP, credits, XP/credits, or a Morality adjustment.

Yeah, Force and Destiny is different from EotE and AoR in that you don't have to "pay" to get extra starting XP or Credits.

Like The Shy Ion said, you simply pick one of the listed options as your PC's Morality bonus. And unlike EotE or AoR, you can't stack effects*, though for Edge/Age you'd need a rather small party to have an Obligation/Duty value high enough to allow you to do so.

*For instance, if your character's starting Duty is 15, you could go +10 XP and +1000 credits, thus reducing your starting Duty to 0. Or you could get both the XP awards for an extra 15 XP at character creation.