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
In MnO4- the four oxygens total -8, so manganese must be +7 for the whole ion to carry a charge of -1.
The mistake people actually make
A positive standard cell potential means a spontaneous galvanic cell; a negative one has to be driven, as in electrolysis. Electrons travel through the wire, while the salt bridge carries ions.