How step-up / step-down transformers work considering that you cannot create or destroy electrons?
Electrons aren't created or destroyed, they just move around.

Have a look at a diagram of the transformer: (from Wikimedia Commons)



Electrons get pushed into the red coil, and out the other end of the red coil. This causes different electrons to be pulled into the blue coil, and pushed out the other end of the blue coil. At no point are electrons created or destroyed.