Configuring gridsets
Gridsets are caching schemas. When you decide to store tiles for a layer, you have to define the common properties for the tiles set. The logical entities where you store those properties are the gridsets.
The properties you can configure in a gridset are the CRS, the tile sizes in pixels, the number and scale of zoom levels, and the bounds of the gridset. Once you define a gridset and bind it to a layer, your client requests must conform to the caching schema, that is, the gridset or GeoWebCache will be unable to fulfill your request.
For your convenience, GeoServer comes with a common gridset already configured.