Idiophones are perhaps the oldest musical instruments in history. Simply put, idiophones are any instruments that naturally make a pleasant sound due to the materials they are made of. The earliest example is more than likely to rocks or sticks being struck together. Normally, they achieve their sound through hitting, but some examples make sound through simple movements. Today, they fall into the percussion section and include woodblocks, bells, cymbals, xylophones, rattles, and gongs.
Also in the percussion section, membranophones are instruments that that make sound from tightly stretched membranes over some sort of frame. The size and shape of the frame combined with the thickness and tightness of the membrane are what create the individual tones. These include: snare drums, bass drums, bongos, tambourines and congas. Normally, you hit these instruments with sticks or your hand, but the kazoo falls into this category, because the membrane creates the tone, rather than the air you blow through it.
Aerophones are perhaps the broadest types of instrument. By definition, an aerophone is anything that achieves the desired sound by forcing air through the instrument, which creates vibration. Some of these instruments, like saxophones and clarinets, achieve the vibration through reeds that are attached to the mouthpiece. Flutes achieve the vibration by forcing the air to strike a sharp edge. Both the brass and woodwind sections of an orchestra fall under the aerophone type. The pitch and tone of each instrument is determined by size and shape of the vessel and can be controlled by the musician through holes, valves, and keys. Other aerophones include the trumpet, tuba, harmonica, trombone, recorder, oboe and bagpipes.
Chordophones are instruments that make sound when stretched strings vibrate. Normally, these strings are stretched over some sort shell or body to maximize reverberation. You can play these instruments by plucking, strumming or through friction from a bow. The harp, violin, cello, fiddle, guitar and banjo are all chordophones. All of them fall into the string section of an orchestra.
Some instruments cross over into two different families. You can classify the piano, for instance, as a stringed instrument because its sound originates from the tightly stretched and precisely tuned strings inside the body. However, these strings are struck by hammers to generate the vibrations and therefore can be considered a percussion instrument. Musicologists agree that the piano is actually a hybrid and is considered to be a "keyed zither."