How do you extract aluminium from Aluminium Oxide?

By Electrolysis.

Aluminium is too reactive a metal and too high in the reactivity series to be reduced by carbon reduction.

The method is to dissolve aluminium oxide in cryolite(a temperature reducing catalyst).

An electrical charge is put across the mixture

Whereupon the aluminium oxide forms the cation Al^(3+) and the oxygen forms the oxide anion (O^(2-)

The aluminium cation moves to the cathode and received electrons from the electrical charge at the cathode to form aluminium metal.

Correspondingly thre oxide anion moves to the anode and forms oxygen. However, because of the high electrical amperage , the anions if very hot , and made of carbon, so the oxygen reacts with the anode nnd forms carbon dioxide, which the released gas.

Have a look and the Royal Society of Chemistry's video on this industrial process.