How the ideas connect
A good science page should make the connection visible, not just list definitions.
Oxidation and reduction
Redox reactions involve electron transfer or, more generally, changes in oxidation state. Oxidation and reduction always occur together.
Tracking oxidation numbers is a practical way to see which species loses electron density and which gains it.
Galvanic cells
A galvanic cell converts the free-energy change of a spontaneous redox reaction into electrical work by separating oxidation and reduction into half-cells.
Electrons travel through the external circuit while ions move through the electrolyte to maintain charge balance.
Electric potential
Electric potential is potential energy per unit charge. Potential differences tell us how much electric potential energy changes per unit charge between two points.
Voltage is therefore not a substance flowing through a wire; it is a difference in electric potential.
What to notice
A good science page should make the connection visible, not just list definitions.
Sources
IUPAC Gold Book · NIST · BIPM