system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do transformers work, what do they do, and why do we use them?
gpt
Electricity and magnetism are two sides of the same coin.  An electric current running through a wire creates magnetism.  A wire moving through a magnetic field creates electricty.  There's not much of a difference between a generator and a motor.

If you switch from DC to AC, you get some more interesting & complex electromagnetic fields.  An AC current moving through a coil of wire creates an EM field.  Another coil of wire placed next to that will start generating an electrical current.  It's technically called "induction" but for our purposes, it's a little bit like radio.

A transformer is just two coils placed next to each other.  By picking the right size coils on either side, you can "step up" or "step down" the voltage.  A good example is the standard 'wall wart' that runs most electronics.  You get 110 volts out of the wall but you only need 12 to run your laptop - a simple transformer takes care of fixing this.

If you want a visual explanation...  Imagine you have 2 fans facing each other.  One of them runs, the other just sits there and spins.  If you have different sizes of fans, the 'passive' fan will spin faster or slower than the 'active' fan.