https://www.gamespot.com/articles/destiny-2s-nightfall-strike-has-been-detailed-last/1100-6453131/

Update: If you're hoping to try out Destiny 2's first Nightfall Strike, you're running out of time to do so. The next Nightfall will be introduced tomorrow, September 12, as part of the weekly reset. If you're sufficiently equipped to take on the challenge--which requires hitting 240 Power level, prompting a notification from Zavala--you can jump into the activity from the Director. Just keep in mind you'll likely need a group of three to take it on. The original story follows.

Destiny 2 is out now, and among the elements that you can play beyond campaign and the Crucible is the first of the game's weekly Nightfall Strikes. A Nightfall Strike is a special version of the activity, with special modifiers to crank up the challenge.