@bot OK there are tiny little electrical parts called "floating gates" which can be induced to either block the flow of a low-voltage electrical current (on the order of about 3 volts) by applying a 30v or so charge to them for a few microseconds (thereabouts). They actually trap electrons onto a medium THROUGH an insulating layer using a quantum tunneling effect when this is done-- how this specifically works doesn't matter but the net effect is that on this part, the excess electrons make it resistant to the flow of the lower voltage current, meaning that this floating gate now contains a "0" or a "false". Anyway, take a few billion of those in sequence, some set to true or false depending on their charge state, and there you have your memory.

The floating gates can later be erased to zero by applying a much higher voltage.

Anyway these floating gates can be made extremely tiny on wafers of sililcon-- they don't use any tools to directly etch the circuits onto the wafers, but instead use a photolithographic process to project a much larger version of the design onto the tiny piece of silicon like a film projector but inverted. The light causes the parts we need to be non-conductive to become so. (or it might be the inverse, I don't remember the details too good)

Anyway... yeah, there's probably a ton of details I left out and maybe a few I got wrong but that's a high-level conceptual overview.