The principles behind the asset system are the following:
Ultimately, the asset system is a way to hide the real files to the user, so the engine can use more creative solutions when it comes to file management, while the users are only concerned with the concept of an asset, i.e. a piece of data that can be created, modified and submitted to source control.
The user documentation of the Asset System can be found here: Asset System 5.5.2
As a programmer in the Sandbox, what this means for you is that the asset system is primarily a unified file management service that provides the following features to you "for free":
This means you should not have to do any of that work except implement the relevant methods in your specific AssetType and AssetEditor, i.e. the specific part of your system.
Let's go over the most important use case of having to interact with the asset system: adding a new editable asset type.
Create a class and inherit from CAssetType. Implement all the virtual methods to describe your type, implement importing if necessary, and editing if necessary.
A good example of this can be found in the SamplePlugin in SampleAssetType.h/cpp. These files will be updated if the API changes.
Adding an asset editor
Create an editor class inheriting from CAssetEditor. This is an advanced version of CEditor that offers similar services and then some more related to editing assets. Implement all the virtual methods necessary and you are done, your asset can now be edited.
A good example of this can be found in the SamplePlugin in SampleAssetEditor.h/cpp. These files will be updated if the API changes.
If your asset is imported from an external tool such as a DCC, you may also need to write an Asset Importer.