This setting is needed to Run on Physical Device.
This tutorial shows how to enable Automatically manage signing which takes care of creating certificates and profiles.
Certificate is electronic document that identifies you as an iOS developer and is valid only for a specific amount of time.
Apps that you want to put on your iPhone must be signed with your Development Certificate.
Creating Development Certificate is free.
Apps that you want to submit to the App Store must be signed with Distribution Certificate.
To create Distribution Certificate you must be a member of the paid Developer Program.
For each app you also need Provisioning Profile which is used to sign app for use on your particular device (or devices).
Project Navigator
Select Project Name (opens Project Settings)
Tab: Signing & Capabilities
Automatically manage signing: ON
Team: (select your Apple ID)