Micro Evolution is variation within a species such as variations in proportion and color etc.. If these small variations in proportion, color, breeding habits, diet or anything else lead to the population bearing that trait in common becoming segregated from related population then they would become a sub-species. If they continue to diverge such that they were no longer able to breed with any related population then they would become a completely different and separate species being that they are now also genetically isolated from related populations.
Macro Evolution is variation between species, such as when the small variations within a population lead to more dramatic variations from related populations for instance. Micro evolution thus is just small steps towards Macro evolution.