How to use onGigyaServiceReady() ?

In our Ui5 application, we are using Gigya Screensets in different controllers. As per the Gigya documentation available, we are to declare all gigya related functions in one handler and call it in onGigyaServiceReady().
We are calling the Gigya WebSDK in index.html file.

Are we supposed to declare all the functions having Gigya API Calls in onGigyaServiceReady function? If not, then how do we ensure that all Gigya APIs are executed once the Gigya WebSDK is loaded.