Creating necessary policies for the Azure Active Directory B2C tenant
After creating an entry for B2C on the Identity Provider end of things you should return to the B2C portal.
While you could certainly integrate your apps directly with the IdPs the whole point of B2C is to abstract this away from the apps and have a middle layer handling this complexity. For this reason configuration must be done in the form of setting up policies in the portal that dictates how sign-up, sign-in and profile editing works. Let's go through setting up a basic setup.
Next thing we need are signup policies. These control the requirements for signing up/creating an account in the system. While the user will already have an account with an IdP they also need an entity in your app.
Click "Add" and start by adding "Google" to the "Identity providers" section.
The we need to select which attributes we collect as part of the sign up process. If the IdP provide these AAD B2C will collect these, but if the IdP doesn't supply everything the user will need to type it in manually.
This concludes the setup part of things, and the next part is writing apps to take advantage of the configuration shown above.