Redox and cell potential
Oxidation is loss of electrons at the anode, reduction is gain at the cathode, and cell potential is cathode minus anode.
A worked example
Cell notation reads left to right as the physical setup: anode | anode solution || cathode solution | cathode. For Zn(s) | Zn2+(aq) || Cu2+(aq) | Cu(s), the single line after Zn(s) marks the solid-to-solution boundary at the anode (oxidation, Zn -> Zn2+ + 2e-); the double line is the salt bridge; the single line before Cu(s) marks the solution-to-solid boundary at the cathode (reduction, Cu2+ + 2e- -> Cu). Whichever metal is written on the left is always the anode.
The mistake people actually make
A voltaic cell generates current from a spontaneous redox reaction (E°cell > 0); an electrolytic cell forces a non-spontaneous one using an external power source. The electrode definitions don't change -- oxidation is always at the anode, reduction always at the cathode -- but which electrode is positive flips between the two, which is the single most common PAT mix-up on this topic.