In the same way, when a sound source is activated (for example when a bell moves) this causes the surrounding air particles to vibrate, thus creating a sound wave.

The sound pressure waveform is set up by the molecules being squeezed together (condensation) and then moving apart (rarefaction). The air pressure changes caused by these vibrations propagates through the air in a similar way to the waves in water with the pattern of vibration being spread outwards from the source.
The sound pressure wave contains areas of alternating low and high pressure. If this wave reaches the ear it causes pressure changes within the ear, that in a normal ear will be interpreted as sound.

What is a pure tone compared to noise?

A pure tone : one frequency features the vibration. (p = period)	Noise : opposit to a pure tone, with no specific frequency