If this is the first time developing extensions for Content Services it might seem a bit daunting at the start. However, if you are a Java developer you should be able to quickly get up to speed on the platform. Content Services is implemented in Java and most of the extension points use Java.
It’s a good idea to start your developer journey by reading through the Software Architecture section, as this will get you up to speed on the different components of the platform, and how they work together. It will also introduce you to the different types of extensions that can be implemented.
Designing and implementing a content model is usually the first thing that needs to be done in most content management projects. So make sure to read through the Content model extension point documentation and then walk through the content model tutorial. By implementing a content model you will get familiar with the in-process extension model and the associated SDK 3.
When you have the custom content model in place, providing types and aspects related to the project domain (i.e. finance, healthcare, manufacturing etc.), then you can move on and implement the business logic and the user interface with the Alfresco Application Development Framework (ADF). ADF is based on Angular, and it provides a number of components that can be aggregated to create the user interface you need for your domain.
If you need to implement business processes that will process the content in domain specific ways, then have a look at Alfresco Process Services.