By now you should understand the fundamental concepts of how a Projection works by reading about its use cases. This guide will briefly describe the basic components of a Projection and instruct you step-by-step on how to build a functioning application.
The example used in this guide is based on a more complete application that is part of the Microservices with Akka tutorial. It builds a full CQRS (Command Query Responsibility Segregation) ES (Event Sourcing) system using a combination of features from the Akka toolkit.
This video on YouTube gives a short introduction to Akka Projections for processing a stream of events or records from a source to a projected model or external system.