When the iPhone X was announced to have absolutely no home button, this raised a number of questions. How do you access Siri? How do you do screenshots? How do we even get to the home screen? Wait… how do we enter Reachability (one-hand mode)?
The new iPhone’s interface is entirely gesture-based, and to return home, one simply needs to swipe from the bottom up. There is a black bar down there, conveniently placed to show us that a gesture is available. And while many thought that Reachability is gone, since there’s no home button to tap to activate it, it seems this black bar is also used … – Source