After you create your app, we need Certificate and provisioning profile for building your app. Follow the steps below to generate Distribution Certificate.
2.Go to https://developer.apple.com/account/ios/certificate (log in if necessary).
3.To add a new certificate, click +.
4.Under Production, select App Store and Ad Hoc and click Continue.
6.Click Choose File, browse to the .csr file that you downloaded in step 1 and click Open.
9.Return to Appmaker, click browse and browse to the .cer file that you downloaded in the previous step.
If you still feel confused checkout this video on How to create an IPA file