When creating an app, you'll need a App ID. This is used in a number of places – think of it as a unique name for your app, that will be included in our next step (creating a provisioning profile).
If you aren't already signed into your Apple iOS developer account, sign in using your authentication details.
Click Certificates, Identifiers & Profiles on the right of the screen
On the next page, click on Identifiers.
Click on the plus button at the top right
Enter a descriptive name for your App ID.
Leaving the Explicit App ID choice selected, enter a unique identifier. The usual convention here is to create a identifier of the form com.yourcompany.yourappname
Make sure to check the Push Notifications option at the bottom of this form, if you require push notifications to your App's users.