Before you can create a signing certificate and a provisioning profile, you have to register your app in the Apple Developer portal. The AppID is used to identify your app with Apple.

This do this, simply follow these steps:

1. Log in to Apple Developer at https://developer.apple.com/membercenter/
2. Click on Certificates, Identifiers & Profiles
3. Click on Identifiers
4. Click on the PLUS icon
5. Under App ID Description enter the title of your app
6. Under App ID Suffix choose the Explicit App ID
7. Under Bundle ID enter the app identifier your have configured inside Aquro App Studio (read more about app identifiers here)
8. Under App Services select the services you wish to use inside your app (normally the default selected services are enough)
9. Click on the Continue button
10. Read the confirmation and confirm by clicking on the Submit button
11. Your AppID will now be generated