Data Persistence (CRUD) in Umbraco
The Umbraco Services layer is used to query and manipulate Umbraco stored in the database.
Service Context
The ServiceContext is the gateway to all of Umbraco's core services. In most cases, the ServiceContext will be
exposed as a property on all Umbraco base classes such as SurfaceControllers, UmbracoApiControllers, any Umbraco views, etc...
So for the majority of cases, you can access the services by using this code (for example):
Services.ContentService.GetById(123);
If you are not working with an Umbraco base class and the ServiceContext is not exposed, you can reference the static Current class directly:
Umbraco.Core.Composing.Current.Services.ContentService.GetById(123);
Services
There are a few different services exposed on the ServiceContext such as: ContentService, MediaService, MemberService, etc... There is a service for each type of data in Umbraco.