Flume Sinks are implementation of Sink interface, that are responsible for sending the Events to next Source or write it to a persistant store like File System or HDFS or even a DB.
A Sink can be associated with one or more Channels. Each Sink implementation has an associated SinkRunner, which is responsible for driving the Sink.
The core processing i.e. writing the Event to Store or forwarding to next Source, happens in process() API of Sink implementation.
Flume comes bundled with following Sinks