In the top-left corner of the screen, you will see a blue + sign; click on it.
Before you enter any of the information, click on Developer Portal at the bottom of the window. This allows you to set up the Bundle ID before creating the application.
Once at Developer Portal, the App ID Description can be the name of the application. The App ID Prefix should be filled out for you. I will use Team ID. I used Explicit App ID and used the reverse-domain name style:
com.mycompanyname.appname. For App Services, I will use Game Center and In-App Purchase:
Click on Continue.
On the next page, Confirm your App ID will display ...