Hearing aids work differently depending on the electronics used. The two main types of electronics are analog and digital. All hearing aids, regardless of technology, are designed to increase the volume of sounds reaching the ear by electronic amplification. In order to achieve this, a hearing aid needs three basic components:
One or more microphones to gather sound waves and convert them to electrical impulses
An amplifier to increase the strength of the signal
A miniature speaker, which converts that electric signal back into acoustic energy, producing amplified sound waves that travel directly to your eardrum.
The difference between analog and digital hearing aids is how the energy is amplified.