Oxidization, Reduction questions

[NeedBeer]

Hi im currently a chem 30 student, and right now we are doing a unit on oxidization and reduction. I understand the stoich involved and the process of the problems, but when it comes to the theory im lost. I know that an oxidizing agent loses electrons, and a reduction agent gains electrons, but im still quite confused by the following. An SOA is actually the reduction half reaction? why is this? An SRA is actually the oxidizing half reaction? can anyone explain to me why this is? And what do oxidizing numbers actually mean ( ex. O = -2) Can someone try to explain this to me, my teacher is useless. thanks