How can I delete open apps in my iPhone X ?

If you mean close them so they aren't "running" as opposed to completely deleting them from the iPhone,

Then simply swipe up from the bottom and stop halfway through the screen, while holding your finger on the screen to enter the multitasking mode.

Then press and hold on one App, until an ✖ appears in the corner, you can then either tap the ✖, or swipe the app up and off the screen.

How to force an app to close on your iPhone, iPad, or iPod touch - Apple Support

Hi

Go to i books download ios 11 user guide &iPhone X guide.

Cheers

Brian 🇬-1F1E7;