Some aircraft have only a single tire. Gliders are the most common example of single wheel planes. The pilot must balance a glider on the single wheel during takeoff and landing.
Airplanes called "tail draggers" have two main landing gear and a little wheel or skid on very rear portion of the plane. Tail draggers are steered on the ground with the rudder and require some very specific flying skills when taking off and landing. The infamous "ground loop" happens to the inattentive tail dragger pilot.
The modern landing gear style is the tricycle with two main landing gear and a nose gear. The steerable nose gear makes the tricycle geared airplane easier to steer on the ground. Takeoff and landing with the tricycle style gear is easier to learn than with the tail-dragger. A ground loop is not possible with this style of gear.
An airplane's landing gear is either fixed or retractable. Retractable landing gear increases performance and fuel economy by reducing airflow drag. It also ads cost and complexity. A pilot who is switching from fixed gear to retractable needs to make certain to remember to lower the gear before landing.
Military aircraft have all sorts of interesting landing gear configurations. The B-52 "Buff" cold war bomber has four sets of tires like a beverage cart. All four sets are steerable. The Buff also has wheels attached to the wingtips that fall away during takeoff.
