Class B airspace is for BIG airports (think Class B for Big). This is the airspace around the busiest airports in the United States. The airspace is made up of several layers that get wider and wider as you get up in altitude. Generally, it is recommended to think of Class B airspace as an upside-down wedding cake (graphic below), although Class B airspace is generally customized for each airport to account for the flow of aircraft landing and taking off at the airport.
Before entering Class B airspace, aircraft MUST receive prior ATC authorization. Manned aircraft are typically required to be equipped with a Mode-C (altitude reporting) transponder.
The typical ceiling for Class B airspace is 10,000 feet MSL (mean sea level, not above ground level) – remember this for the exam!
Class B airspace is depicted on sectional charts by a solid blue line (see image below).