First of all a distribution certificate will need to be created. This is a one off step as the certificate will be used for all of your apps you want to deploy on iOS. To create this certificate login to https://developer.apple.com/ and select the link to Certificates, IDs & Profiles.
From here you will be shown a menu allowing you to select Certificates, Identifiers, Devices and Provisioning Profiles. Under the Certificates heading select the Production option.
On this page click on the plus icon. From here a new page will be shown, select the App Store and Ad Hoc option and follow the on screen instructions.
When you have completed this process you will have a distribution certificate installed on your Mac.