Quarz crystal is a component that can be used in an oscillator circuit to generate a signal of the crystal's frequency..
You can also find so called crystal modules which basically are oscillators packed in DIL16 or similar housings and have an oscillator circuit and crystal quarz built-in ..
thnks,
can you introduce a simple circuit that uses the crystal as an oscillator? and what r the impotant thing for oscillation to start (practical things)?