my iphone x touch works on its own sometimes why?

Read these support guides:

Use Touch ID on iPhone and iPad - Apple Support

or

Get help with Touch ID on your iPhone or iPad - Apple Support

If nothings helps, have your iphone inspected at the nearest Apple Store.

Regards

Giulio

Sorry, I've confused touch screen with touch id (my previous answer was not for you).

If you have this kind of problem, try a forced restart of your device with the following steps:

On an iPhone X, iPhone 8, or iPhone 8 Plus: Press and quickly release the Volume Up button. Press and quickly release the Volume Down button. Then, press and hold the Side button until you see the Apple logo.

If nothing helps, since your device is brand new, contact your nearest Apple Store and have your iPX inspected.

Regards

Giulio