If you've chosen Redis at instance creation time, then you'll have a Redis server available. This instance of Redis can be access from any of your shared instances. Redis is not exposed to the Internet.
Redis data is not persisted. Redis on Amezmo is designed to be used for in-memory caching only, and long-term data should not be stored in Redis, as it will be lost upon restarting your instance. You must use a database for persistent storage.