On Xbox: say "xbox, bing destiny" it should be one of the things that pops up (expansion 1: dark below") select it and there should be a purchase option. Alternatively if you plan on getting the next dlc slated for an early 2015 release choose the expansion pass to save 5$. Note: you can also use xbox.com and search destiny. On PS: Go to PS store (either online at store.sonyentertainmentnetwork.com or on your console) search destiny expansion choose "expansion 1:dark below". There should be a purchase option. And again if you plan on getting the next dlc slated for an early 2015 release you can choose the expansion pass to save 5$. Hope this helped.

So you cannot use Microsoft points to buy this if your Xbox 360?

Xbox should use your Microsoft points before switching to national currency which it should have transitioned to