I've read all the docs on the Google Cloud SQL site, and I now understand how to created and manage Read Replicas, but I have not seen any information about how to use them,
Does Google automatically load-balance connections between all instances?
No, it doesn't. Each instance is independent. You can connect to replicas and use them to read while using the master to read/write, but you need to design that logic into your application
Do I have to manually connect to a specific Read Replica to avoid hitting the Master? If so, do I have to manage reconnecting on replica failure myself?
Yes, you have to connect to a specific read replica. Right now you can't even save and reuse the instance IP like you can do with compute engine instances (sigh, I hope they fix this soon....).
There is now a failover replica option that you can use so you don't need to connect to the read replica yourself, but it only activates on failure, it is not a load balancer.