As mentioned previously, the included GeoWebCache comes with a default configuration. From the web interface you can manage almost all parameters; this is a brand new feature of the GeoServer 2.2 release. In earlier releases, you had to go to the GeoWebCache web interface or open the configuration files.
The Caching Defaults form includes general parameters. The first section is about services used to expose tiles.
By default, the first option is disabled. Direct integration is about the endpoint used in WMS GetMap requests. If you go with the default option, you will have to use a custom endpoint to tell GeoServer that you want to retrieve a map from the cache, if there are tiles available to fulfill your request.
http://localhost:8080/geoserver/gwc/service/wms?
Enabling direct integration lets you use the same syntax you would use against a non-cached layer:
http://localhost:8080/geoserver/<workspace>/wms?tiled=true
Apart from the endpoint...