What is the use of entitlements.plist file?

Entitlements are announcements that “I am gonna use this feature like APPLE PAY” and provision profile will say, “Yes dear you can use Apple Pay Feature”.

Entitlements are part of the code-signed app.

1. The entitlements file defines certain capabilities of your app. Usually, the file is automatically generated by Xcode when you enable a capability for your app.
2. You only need the file if you enable certain capabilities, e.g. Healthkit integration. If you'd like to use these features, you have to add it. Otherwise, Apple will reject your app.
3. You can name the file like you want. You can also rename it as long as the build settings point to the correct file name for it.

myApp.entitlements is Xcode generated plist when you enable capabilities (e.g push notification) for that particular target.