Log into your iOS Development account and click on the iOS Provisioning Portal link at the right hand side of the page. In your Provisioning Portal, click Certificates in the left tab bar. If you do not have a certificate, there will be an option to submit one. To do this you will need to make a Signing request. You can do this by launching Keychain Access, located at /Applications/Utilities. Then go to Keychain Access > Certificate Assistant > Request a Certificate From a Certificate Authority. Enter your email address and your name, then select save to disk. Once that has been generated, go back into the certificates page of your provisioning profile and submit it for approval. After the certificate gets approved, download the file and open it, and it will be added to you keychain access.