A galvanic cell
In the external circuit, the electrons flow
from the zinc electrode to the copper electrode.
The half-reactions are:
Zn Zn2+ + 2e¯ (as the zinc electrode is negative)
Cu2+ + 2e¯ Cu (as copper is the positive electrode)
the overall reaction is the sum of these,
Zn + Cu2+ Zn2+ + Cu