Answer:
To put it simply, redox (reduction/oxidation) reactions are a transfer of electrons. In it's most simple form, as a half equation, Cu -> Cu2+ + 2e-. Or as a complete reaction, Zn + Cu2+ -> Zn2+ + Cu. The electrons are not written in the full equation because they cancel out:
Cu2+ + (2e-) -> Cu
Zn -> Zn2+ + (2e-)