I have a code for the DLC Season Pass for Xbox ONE, but have no idea how/where to enter this to be signed up? Can't find anything online and already contacted Bethesda and got a general automated response that also didn't help. Anyone?

I have not used on on the new Xbox One interface. I believe you need to go to store section and there should be an option in there to redeem codes

Season Pass codes can be redeemed from the Xbox Live store. If you go to store and then select "Browse All Games", you should see an option for "Use a Code" at the top of the page.

We'll be sharing more details on Fallout 4 DLC next year.