Classes list different types of the the same layer. For instance, Parcels may be zoned into many classes like agricultural, residential or commercial.

The extent of the map is the area that is visible in the map window. If your current extent includes the whole county, you would decrease your extent to see only 4 townships in the map window.

Items that are displayed on the map. Examples could be rivers, roads, counties, townships, parcels or many others. Features are usually the items of interest on the map.

A Group is used to organize related layers. For instance, the Transportation group contains the layers related to transportation such as roads and railroads.

This is a grouping of related map features. An example would be Railroads. Railroads is a layer that is located under the transportation group.

This is another name for search. You can seach layers that are listed in the active layer dropdown in the upper right corner. To make a query, you must use the Information Tools.