Too Long; Didn't Read
The main part of the certificate is your public/private key pair, which is a guarantee that the apps are truly developed/distributed by you. There are two types of certificates: Development and Distribution. The development one is used when you want to install the app using XCode (when developing an app), and the distribution one used for distribution of the application (TestFlight/AppStore) Every certificate and provisioning profile have an expiration date, so it’s really important to check it before using any.