Somebody may show up to correct me on this, but from what I've gathered, microevolution involves shifting around of existing genes and changes in gene expression, as is the case with animal breeding; whereas macroevolution involves actual genetic mutations.
Micro-evolution is the same thing as natural selection and relates to variances within a species. In the wild, those who have the most advantageous characteristics are more likely to survive and reproduce. for lack of a better phrase, it's survival of the fittest.
Macro-evolution would be the appearance of a new species out of older ones and the change would be so significant that the the 'new species' would not be able to reproduce with the 'old' one.
Evolutionists claim that this 'speciation' occurs over a long period of time. The physical reality is that this is a myth unsupported by the facts. The reality is that what they call 'speciation' must occur at some point between one set of 'parents' and their offspring. even they know this is a ridiculous suggestion, but they cannot explain how it could be otherwise other than to say it is a result of gradual changes. Of course, there is no evidence for it; but they believe it anyway.