Suppose we have the "basic" stuff like a battery 2 piece of wire and a bulb. Battery has a potential difference. But from where electrons flow to make the bulb light? from wire or from battery or from both? also if electrons flow from battery and they go through the wire (conductor) then why in insulators this doesnt happen? insulators dont give electrons but why they dont let electrons flow?
Every piece of the circuit has the molecular structure in which the electrons can either be bound to its atoms nuclei or they have enough energy to detach from their atom and roam in the field of metallic bond. Conducting metals have low energy threshold that electrons need in order to detach. A force caused by a potential difference can direct their collective movement and therefore we have a stream of electrons or an electrical current. Now, insulators are structured in a way that their electrons must have a greater energy in order to be detached from their own atom so, in standard conditions, force by a potential difference won't be able to move electrons bound to their atoms and therefore there is no electrical current through the insulator material.
Electrons from the material in the entire circuit flow. Conductors are different to insulators because their atomic structure is made of a “sea of electrons” around the positive nuclei. These electrons are free to move from atom to atom in the conductors and not in the insulators. This may be better explained why by a chemist, but I believe it’s a property metals near the “center” of the periodic table have (I’m probably not technically right about this).